I have been having a lot of problems with DMD locking up on me this past week. I think that it only happens when I am online with a PLC. I do know that the odds of it happening are indirectly proportional to how much time I have available. Typically it takes a reboot to get it working. Sometimes I am able to restart DMD and it will work.
It is running on WIN7 Enterprise in VMware.
Send one of more of the dump files to support@hosteng.com. If you can give us any guidance into what you are doing when it happens, that would be great. Also, how are you connected to the PLC?
Since it is the DmD process crashing, it's probably leaving the Comm Server process running in an awkward state. If you will pull up Task Manager and kill the CSMain process, you should be able to run again without rebooting.