The error message
Msg 2601, Level 14, State 1, Line 3
Cannot insert duplicate key row in object ‘%.*ls’ with unique index ‘%.*ls’.
is a run time error of severity level 14. This error message appears when you try to insert an already existing value into a unique key column. Duplicate key values are not allowed in a unique key column. The data that you want to insert is prepresent, hence it can not be inserted.