# Error 128 (ref to unknown data)

**URL:** <https://tech-community.robotics.abb.com/t/error-128-ref-to-unknown-data/2536>\
**Category:** RobotStudio\
**Created:** [February 24, 2009, 2:13pm UTC](https://tech-community.robotics.abb.com/t/error-128-ref-to-unknown-data/2536 "2009-02-24T14:13:16Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![drdeason21](https://avatars.discourse-cdn.com/v4/letter/d/b5e925/32.png) [@drdeason21](https://tech-community.robotics.abb.com/u/drdeason21)\
**Post date:** [February 24, 2009, 2:13pm UTC](https://tech-community.robotics.abb.com/t/error-128-ref-to-unknown-data/2536/1 "2009-02-24T14:13:16Z")

</div>

I get error 128 when I reference any Digital I/O signal in the program (offline tab) of Robot Studio. I have checked and rechecked to make sure the signal is defined.

Error 128 : Reference error : Reference to unknown entire data doPurge

Any ideas why Robot Studio doesn’t recognize my I/O?