labview error

[berkay.coban]

LabVIEW: Null window.

The top-level VI"denproj.vi" was stopped at unknown on the block diagram of "popup.vi" 
I am trying to call another vi from the main vi in ​​labview but I get this error.

[rolfk]

Without the VI in question attached to your post, the only thing we can do is to Google, something which you could do too, you know.

https://letmegooglethat.com/?q=LabVIEW%3A+NULL+windows

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000001DcZdSAK&l=nl-NL

https://forums.ni.com/t5/LabVIEW/Labview-Null-Window-stopped-at-unknown-on-the-block-diagram/td-p/10...

https://forums.ni.com/t5/LabVIEW/LabVIEW-Null-window-error-in-an-application/td-p/2539028

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z000001DcZdSAK

There are more links in Google that seem relevant, but these should be more than enough already.

[Yamaeda]

Why Do I Get a "LabVIEW: Null Window" Error When Running My Executable? - NI

[altenbach]

You got excellent advice already, but this error should not appear in the development environment. We must assume that this is a built application. Is it?

The application builder is typically smart enough not to remove the front panel for any VI that needs to show it, so we must to conclude that your popup.vi is called in an unusual way.  However, the information you provide so far is too sparse to offer specific advice.