Error : btnLogin

I downloaded PMU on my computer recently. Whenever I attempt to log in, an error message pops up saying ‘Not found @ btnLogin.’ After closing out / pressing okay, the program will stop working and close. My software is up to date, so I doubt that is the issue. Thank you for your time!

what anti-virus do you have? there have been issues with Kapersky and Norton removing important files for the game to run without permission of the user, leaving the game unplayable unless the user tells the antivirus to leave those select files alone.
there are no viruses within the game, but some anti-virus are very sensitive to various sorts of files within games/downloads.