Jason Brimhall explains an error message which might be confusing at first:
Here is the error message that is quite possible to encounter while creating principals.
Msg 15006, Level 16, State 1, Line 6
‘SomeDOmain\jason’ is not a valid name because it contains invalid characters.At first look, this error makes absolutely no sense. The error states there is an invalid character somewhere in the string “SomeDomain\jason”, yet every character in that string is supported and normal for the collation. This can be a head-scratcher for sure.
Read on for the answer.