VirtualWin- Failed to register hotkey

Hi boys and girls,
I have some concern here regarding VirtualWin. I see an error while I am adding some hot keys. Below is the screen shot of the error.
VirtualWin- Failed to register hotkey1, check hotkeys.
I am wondering why I can't add some hot keys in it. I already added some hot keys before successfully, that is why I am thinking what went wrong with this application.
The reason is also not mentioned in the error message and that makes this problem harder to solve.
Please give me your thoughts and ideas on this error message. All your contributions are highly appreciated and thanks a lot for reading.
