SerializationException: Error deserializing element

I am getting an error message by clicking on a button which opens a window based on the selected name of the window from the dropdown:

“SerializationException: Error deserializing element “<c” caused by NullPointerException”

It works fine in designer. However, it doesn’t work when I publish the project.
Any suggestion.

thanks,

What version of Ignition are you running? This sounds like it could be related to a bug that was fixed inversion 7.8.1.