# Error using Expression Tags

**URL:** <https://forum.inductiveautomation.com/t/error-using-expression-tags/14399>\
**Category:** Ignition\
**Created:** [May 26, 2017, 12:19pm UTC](https://forum.inductiveautomation.com/t/error-using-expression-tags/14399 "2017-05-26T12:19:43Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![rafael.ribeiro-marti](https://avatars.discourse-cdn.com/v4/letter/r/71c47a/32.png) [@rafael.ribeiro-marti](https://forum.inductiveautomation.com/u/rafael.ribeiro-marti)\
**Post date:** [May 26, 2017, 12:19pm UTC](https://forum.inductiveautomation.com/t/error-using-expression-tags/14399/1 "2017-05-26T12:19:43Z")

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Hi everyone,

I am having a very strange problem with expression tags.  
Every type of tag (OPC, memory, query, data type instance) are working in the gateway, except for the expression tags. The values of the expression tags return null and the diag says: Quality: UNKNOWN, Last Execution: UNKNOWN, Value: NULL.

And also, if I apply the same logic of the expression tags to a component (a label, for instance) it works fine.

Does anyone have any ideia what is going on?

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**Author:** ![rafael.ribeiro-marti](https://avatars.discourse-cdn.com/v4/letter/r/71c47a/32.png) [@rafael.ribeiro-marti](https://forum.inductiveautomation.com/u/rafael.ribeiro-marti)\
**Post date:** [May 26, 2017, 12:34pm UTC](https://forum.inductiveautomation.com/t/error-using-expression-tags/14399/2 "2017-05-26T12:34:23Z")

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Solved: The problem was with the Scan Class Slow rate. Thanks