From time to time Geany fails to copy the text to clipboard on Windows.
Even Ctrl+X doesn't help. The clipboard gets empty and then no text is passed to the clipboard. Sometimes in other programs I also get the error with clipboard. I suggest the developers to make an "for" loop to try for, let's say, 10 times, to copy the text (save it to clipboard). I think you should get the error status from Windows API. A am a web (php + JS) and VB6 programmer and under VB6 I do as I described -- it works fine for me.
I hope this helps.