Today a user wasn’t able to log in from his Windows machine to a shared folder in Samba. He was said that his user name (from Active Directory) was not found. The system log was logging the security kerberos event ID 14.
After some digging, I found out this thread with the solution:
rundll32 keymgr.dll,KRShowKeyMgr
This shows up a credentials manager window, where we can delete the problematic credentials. After doing this, the user logged in without problems.