Same problem here (which I did not have with previous beta either). Running Win 8.1 (x64). After computer goes (or has been manually set) to sleep, if TPlus 3937 is maximized, I get the same error repeatedly and can only shut it down with Task Manager.
Happily, other issues I reported repeatedly with previous betas regarding the making of thumbnails appears to be fixed in this version. Win some, lose some. :(