For the day you upgraded and any day you've booted your server, there should be a conversion.log created in C:\SmarterMail\Logs (or wherever your log directory is), could you skim this log looking for any lines containing the word "error" or "exception"? You can post a snippet here and we might be able to figure out what it is. If this is something you need immediately, maybe consider sending in a support ticket. If it's not obvious with the snippet we may need to access the server or interface, hence why a ticket may be needed.

Additionally, you may want to try applying the latest minor release (as it looks like you're a couple behind.) This will help move any future support tickets along smoothly during the troubleshooting phase. Please be sure to take a full backup of the install directory and domain data before starting, then simply uninstall the existing build, then install the latest release to the same location.