# Bad\_DecodingError **URL:** \ **Category:** Ignition\ **Created:** [March 10, 2022, 9:34am UTC](https://forum.inductiveautomation.com/t/bad-decodingerror/57055 "2022-03-10T09:34:06Z")\ **Posts on this page:** 1\ **Showing post:** 6
**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:** [March 10, 2022, 1:42pm UTC](https://forum.inductiveautomation.com/t/bad-decodingerror/57055/6 "2022-03-10T13:42:57Z")
Ah good timing. Is this an S7-1500 or S7-1200? There’s some recent threads about this, but it seems you will need to both enable “legacy DataType dictionaries” in the server and if it’s a 1200 you can’t use the “Server Interfaces” to define an address space. > [@Ignition 8.1 Siemens UDT via OPC UA trouble](https://forum.inductiveautomation.com/t/ignition-8-1-siemens-udt-via-opc-ua-trouble/54865/20): > > To make the Solution concrete in case anyone else comes across this issue: 1200 PLCs have a different OPC structure from 1500 PLCs due to the setup necessary on the PLC side. On the 1500 PLC the checkbox “Standard server interface (SIMATIC namespace)” has to be enabled. “Legacy data type definitions” should be enabled on the OPC. Do not use the “Server Interface” method when communicating datatypes and structures on 1500 PLCs --- _[View the full topic](https://forum.inductiveautomation.com/t/bad-decodingerror/57055)._