Cannot modify technicians

Hi,

We are running ServiceDesk Plus 7.5 build 7506 and have 10 technicians created.

They were all imported from the AD as regular users, and I then "upgraded" them to technicians - no problems.

Now, if I try to change group membership or department or anything else on one of these technicians, and then click save, I get this error:

TechName 311 IT Supporter emailAddress 5068 91 0.0 3 {"QueueOfSites":[{"3":{"8":"IT Development","9":"IT Operation"}}]} 9 FAILURE :Login with same name already exists. Please provide different value for Login Name.

Anyone know of this? I've tried deleted all the technicians and adding them again - same error.

Thanks in advance,
Rasmus