# Expression binding temporarily failing at window open

**URL:** <https://forum.inductiveautomation.com/t/expression-binding-temporarily-failing-at-window-open/16931>\
**Category:** Ignition\
**Tags:** ignition79\
**Created:** [February 9, 2018, 12:21am UTC](https://forum.inductiveautomation.com/t/expression-binding-temporarily-failing-at-window-open/16931 "2018-02-09T00:21:03Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![zacslade](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/zacslade/32/3587_2.png) [@zacslade](https://forum.inductiveautomation.com/u/zacslade)\
**Post date:** [February 9, 2018, 12:21am UTC](https://forum.inductiveautomation.com/t/expression-binding-temporarily-failing-at-window-open/16931/1 "2018-02-09T00:21:03Z")

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Hi all,

I have an expression binding on the enabled property of a button, which uses lookup on a dataset client tag. For a moment right after I open the window, I get an error saying that the tag has value -1, and could not be converted to a dataset.

Right now, I have overlay opt-out set on that binding, but I’d like to get rid of the errors in my console. Any advice?

Thanks in advance!

Here’s the expression:

```auto
lookup(toDataSet({SiteConfig/Header Bar/Tabs}),toStr({[Client]Viewing Site}),false, "siteName", "Runtime")
```

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [February 9, 2018, 1:13am UTC](https://forum.inductiveautomation.com/t/expression-binding-temporarily-failing-at-window-open/16931/2 "2018-02-09T01:13:34Z")

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That’s just what you get at startup from dataset tags. Shortly followed by the real dataset when tag polling starts. Consider using the try() expression function to substitute a suitable initial value during startup.