Fixed...Sort of
I kept having this same issue with my Windows 7 Professional installed on Parallels 8 (on MacBook Pro 2011). My VM was connected to a domain, however, I was only able to log into a local username, rather than my domain roaming profile.
What worked for me:
1) Log in as a local administrator account
2) Click Start Icon
3) Click Control Panel
4) Click Programs & Features
5) Uninstall Parallel Tools (after uninstall is completed, VM will restart)
6) Now try logging into roaming domain username (mine let me in)
It seems the Parallel Tools program was causing an issue. I was able to reinstall Parallel Tools after I managed to log back in (requires a restart as well), and it gave me no issues...allowed me to log in even with a necessary restart.
***Side Note: The next day, my VM/Windows 7 had to restart for another program I installed and I ran into the issue above again. I had to repeat all the steps to be able to login into my roaming domain username. I may just forgo using Parallel Tools as convenient as they may seem to be.