Back (X) button not working

[TerraEnvy]

It was working just fine the other day but for some reason my back button on my project has stopped working.
All I can think of that I have done since it was working is compress it for distribution.

By back button I am referring to "X" on the keyboard. I can' open menu go back ect...
thanks in advance
-Terra

 

[Yeyinde]

Restart your computer. It will fix this problem most of the time.