We also have this problem with PopGrabber stopping at midnight. We started to have this problem about 3 or 4 weeks ago and it has happenned three times so far. We are using version 1.0.4.502 and Exchange Server 2007 version 08.01.0340.000.
Stopping Service and then Starting Service does not work. We have to close the program and restart it.

We have seven logfiles configured. Note the seven errors saying "Could not open log file". Also, this error occured at midnight on 4th August. Note the date/time in the log displayed is 29th July. That would be the seventh oldest logfile - is it trying to open and re-use the file? We only re-boot our server once a month - so the program would not have been res-started since it used that file. Is it fully closing the logfiles so they can be re-used?
Any ideas?