# Derived Tag ExpressionEval Error

**URL:** <https://forum.inductiveautomation.com/t/derived-tag-expressioneval-error/31283>\
**Category:** Ignition Early Access\
**Created:** [January 14, 2020, 7:12pm UTC](https://forum.inductiveautomation.com/t/derived-tag-expressioneval-error/31283 "2020-01-14T19:12:53Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mohamad.tayara](https://avatars.discourse-cdn.com/v4/letter/m/977dab/32.png) [@mohamad.tayara](https://forum.inductiveautomation.com/u/mohamad.tayara)\
**Post date:** [January 14, 2020, 7:12pm UTC](https://forum.inductiveautomation.com/t/derived-tag-expressioneval-error/31283/1 "2020-01-14T19:12:53Z")

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Hi,  
I am using ignition 8.0.6 and have a udt opc tag of document type and using derived tag to extract individual variables, the problem is that at random times i get an error Expression Eval on all variables of the OPC UDT, restarting the tag provider , or simply disabling and enabling the derived tag will solve the issue. Is it a bug or i am missing a configuration.  
Thnaks

 ![a1](https://us1.discourse-cdn.com/inductiveautomation/original/2X/4/45970d32a378f9dd08211577f6e088ac070652bf.png) ![b1](https://us1.discourse-cdn.com/inductiveautomation/original/2X/d/d4d6067841efe7d8145db6dd5f2a2361eb3c2ede.png)

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**Author:** ![jpark](https://avatars.discourse-cdn.com/v4/letter/j/a88e57/32.png) [@jpark](https://forum.inductiveautomation.com/u/jpark)\
**Post date:** [January 14, 2020, 9:33pm UTC](https://forum.inductiveautomation.com/t/derived-tag-expressioneval-error/31283/2 "2020-01-14T21:33:46Z")

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try surrounding it with `coalesce(jsonGet({source},"Stat"),False)`

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<div class="post-metadata">

**Author:** ![Ben.Mehmet](https://avatars.discourse-cdn.com/v4/letter/b/58956e/32.png) [@Ben.Mehmet](https://forum.inductiveautomation.com/u/Ben.Mehmet)\
**Post date:** [February 12, 2020, 3:53am UTC](https://forum.inductiveautomation.com/t/derived-tag-expressioneval-error/31283/3 "2020-02-12T03:53:57Z")

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Has there been any development on this problem ?? our ignition (8.0.6) seems to have the same problem and is only cleared once the tag is restarted.