Can't change a user's business unit or reassign a user's records.

I have a parent business unit with multiple child business units.  For all users that are assigned to the child business units, I need to reassign them to the parent business unit (and disable the child business units).  When doing this either in the Business Unit interface or the User interface, the Change Business Unit window says "Also, the current user cannot be moved because this creates authentication issues."  When I try to change it anyway, I receive the error below.  
An error has occured.
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I receive the same error when I try to reassign the user's records.  I have made sure that the user does not have any records assigned to them, and I've even tried removing their roles.
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Are you doing this from the more actions menu on the user LIST?
KSBrAuthor Commented:
Yes, I get the error by going to Actions (or More Actions) then Change Business Unit on both the User List and once inside the users' profiles.  This happens for every user.
Check event log on the CRM server.
Have you established Tracing to see what is going on? has a great tool called CRMDiag4 that can help you get that going.

Also, it can turn on DEV errors, which will give you an "uglier" error, but one that is easier to research.

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