# Cannot read tag in S7-400 PLC **URL:** \ **Category:** Ignition\ **Created:** [April 30, 2026, 10:24am UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330 "2026-04-30T10:24:52Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Reghardt\_Swanepoel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/reghardt_swanepoel/32/67825_2.png) [@Reghardt\_Swanepoel](https://forum.inductiveautomation.com/u/Reghardt_Swanepoel)\ **Post date:** [April 30, 2026, 10:24am UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/1 "2026-04-30T10:24:52Z")
Bit of a strange situation, but Ignition is refusing to read a tag on a PLC that definitely exists. The full tag path is "[SIG01]DB5000,X0.0" (boolean tag). Background: I recently changed the structure of DB5000, after this Ignition refuses to read any tags inside of the DB. It always gives the error: [null, Bad("Bad\_ConfigurationError: There is a problem with the configuration that affects the usefulness of the value."), Thu Apr 30 12:00:51 CEST 2026 (1777543251357)]. There are other tags also being read on the PLC (other DB's as well) and they work fine. What I have tried: - Restarting the OPC-UA module - Removing the OPC Device and re-adding it (using same name) - Connecting to PLC via Kepware to confirm PLC side - This works - Added device 'test' in Ignition OPC using the same connection settings and adding the DB5000 tag - This works - Exporting tags as JSON and deleting them from the designer, then importing them again - Creating a seperate tag with the same DB5000 address - Deleting the DB from PLC and moving to DB5001 - This works (but we need this to be DB5000) - Going online and Deleting DB5000, then downloading it back to the PLC - This doesn't work - Exported all tags in the gateway and searcing for [SIG01]DB5000 tags to ensure there are no duplicate tags Details: - Programmed in Simatic Manager - Connected using S7-400 driver - Port 102 - CPU slot nr 3 (S7-400 CPU with CP card) - Ignition 8.1.37 (b2024013011) - Siemens Comfort Panel accessing the same tags I am hoping there is some kind of cache that is causing this issue, a cache that can be wipe without causing issues to other devices since this is a production system. Tag export: ```python { "name": "JDESI", "typeId": "JDESI", "tagType": "UdtInstance", "tags": [ { "name": "Control", "tagType": "Folder", "tags": [ { "name": "ic_ReqManual", "tagType": "AtomicTag" }, { "name": "ic_Planned", "tagType": "AtomicTag" }, { "name": "ic_ReqAckAlarms", "tagType": "AtomicTag" }, { "name": "ic_ReqAuto", "tagType": "AtomicTag" }, { "name": "ic_ReqStop", "tagType": "AtomicTag" }, { "valueSource": "opc", "opcItemPath": "[SIG01]DB5000,X0.0", "dataType": "Boolean", "historyEnabled": false, "name": "ic_Interlock", "tagType": "AtomicTag" }, { "name": "ic_Warning", "tagType": "AtomicTag" }, { "name": "ic_ReqStart", "tagType": "AtomicTag" }, { "name": "ic_ReqReset", "tagType": "AtomicTag" } ] }, { "name": "Status", "tagType": "Folder", "tags": [ { "valueSource": "opc", "opcItemPath": "[SIG01]Mx151.2", "name": "ps_Running", "tagType": "AtomicTag" }, { "name": "ps_Consumables", "tagType": "AtomicTag" }, { "name": "ps_Stopped", "tagType": "AtomicTag" }, { "valueSource": "opc", "opcItemPath": "[SIG01]Mx10000.6", "opcServer": "Ignition OPC UA Server", "name": "ps_Heartbeat", "tagType": "AtomicTag" }, { "name": "ps_Ready", "tagType": "AtomicTag" }, { "valueSource": "derived", "deriveExpressionGetter": "{source}\u003d\u0027Connected\u0027", "deriveExpressionSetter": "", "sourceTagPath": "[System]Gateway/Devices/SIG01/Status", "name": "ps_Connected", "tagType": "AtomicTag" }, { "name": "ps_Idle", "tagType": "AtomicTag" }, { "valueSource": "derived", "deriveExpressionGetter": "!{source}", "deriveExpressionSetter": "!{value}", "sourceTagPath": "[.]ps_ModeManual", "name": "ps_ModeAuto", "tagType": "AtomicTag" }, { "name": "ps_MaintAM", "tagType": "AtomicTag" }, { "name": "ps_LineDelay", "tagType": "AtomicTag" }, { "name": "ps_MaintPM", "tagType": "AtomicTag" }, { "valueSource": "opc", "opcItemPath": "[SIG01]DB5000,X0.1", "historyEnabled": false, "opcServer": "Ignition OPC UA Server", "name": "ps_BypassInterlock", "tagType": "AtomicTag" }, { "valueSource": "opc", "opcItemPath": "[SIG01]Mx139.0", "name": "ps_ModeManual", "tagType": "AtomicTag" } ] } ] } ``` ---
**Author:** ![Jasmine\_Quick](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/jasmine_quick/32/80380_2.png) [@Jasmine\_Quick](https://forum.inductiveautomation.com/u/Jasmine_Quick)\ **Post date:** [April 30, 2026, 10:47am UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/2 "2026-04-30T10:47:21Z")
Do you have any other tags pointing within that DB, that may have been broken by the change that you made? ---
**Author:** ![Reghardt\_Swanepoel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/reghardt_swanepoel/32/67825_2.png) [@Reghardt\_Swanepoel](https://forum.inductiveautomation.com/u/Reghardt_Swanepoel)\ **Post date:** [April 30, 2026, 10:52am UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/3 "2026-04-30T10:52:50Z")
Currently, no. The DB shrank down from a list of tags to a remaining 2 tags (both booleans) with a few spare tags to fill the required word size. Thus, only the 2 tags that are giving an error still exist. ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [April 30, 2026, 1:37pm UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/4 "2026-04-30T13:37:16Z")
Is there an error in you Ignition Gateway logs like "Error reading S7ReadResponse. Error code NN"? ---
**Author:** ![Reghardt\_Swanepoel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/reghardt_swanepoel/32/67825_2.png) [@Reghardt\_Swanepoel](https://forum.inductiveautomation.com/u/Reghardt_Swanepoel)\ **Post date:** [April 30, 2026, 1:50pm UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/5 "2026-04-30T13:50:43Z")
Hi Kevin, I do not see any alarms, I also tried searching "SIG" in the logs but it comes back as empty. ---
**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\ **Post date:** [April 30, 2026, 1:52pm UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/6 "2026-04-30T13:52:12Z")
You might need to let support take a look. With the old Siemens driver, `Bad_ConfigurationError` only means two things: - invalid address (OPC Item Path) syntax - response from device with an error code (usually 0xFF illegal access) ---
**Author:** ![Reghardt\_Swanepoel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/reghardt_swanepoel/32/67825_2.png) [@Reghardt\_Swanepoel](https://forum.inductiveautomation.com/u/Reghardt_Swanepoel)\ **Post date:** [May 5, 2026, 9:59am UTC](https://forum.inductiveautomation.com/t/cannot-read-tag-in-s7-400-plc/115330/7 "2026-05-05T09:59:50Z")
I received a response from support: You do not have an active support plan on your current license, here is a quote for $20k to upgrade all licenses from 8.1 to 8.3 before we can support (this offcoarse does not yet include the 50% for our redundant licenses) - Yikes! Seems odd since this doesn't look like normal behaviour from the Ignition OPC, for now I have changed the tag config from DB5000 to DB5001 and moved on.