I have xp mode on multiple win 7 machines and have had NO problems for years. Sometime in 12/15? the xp mode in every machine lost "logon credentials". The current value = none.
My best guess that this is secondary to a security update since it hit all three approximately during the same period.
I have looked through all the TechNet blogs that have the same subject but these solutions are not helping and they are all over 3 years old.
Currently I do have one machine up and running but it requires "XPMUser" as user name and the win 7 password. Trying to duplicate this on other machines has not been successful up to this point.
These machines are not in a domain.