I have been very frustrated for the past 3 months, ever since upgrading to Server 2012. Microsoft Fax has been unreliable. The fax service stops frequently with
The Fax Service Provider 'Microsoft Modem Device Provider' encountered a problem and needed to close.
Error Code: 0xC0000005
This error code indicates the cause of the error.
A Windows Error Report was generated with full details about the problem.
The Fax service will restart now.
At first I thought it was the modem. I replaced it, and it seemed to work better for a while, but the fax service kept stopping with that error. What was weird is that some faxes would come through fine. I reinstalled fax services, moved from virtual hardware to physical hardware, thinking maybe there was something about the virtualization that was messing with it.
It turned out to be a bug in FXST30.DLL. I learned about it this thread. It mentions windows 8.1. Evidently this bug is also in recent updates for Server 2012. Not trusting random DLL downloads from the internet, I grabbed the DLL from one of my Windows 7 64bit machines, and problem solved.