vst plugin edit window not showing

Hi there - I have a problem that’s driving me crazy:

In my cubase LE5, I have one vst plugin that won’t show its editing window, when creating an instrument track - thus I’m not able to choose any instrument or setting. No other vst plugins are affected, they all appear just fine. In the windows menu, the plugin is listed as active, but alas: no actual window. I’ve tried resetting the window, reinstalled the plugin - no succes.

I’ve saved another cpr project with this plugin active, and in this the vst’s window works perfectly.

Any ideas how to solve this problem?

Best wishes, Sorbus