Symptoms

Receiving the error above when logging into a K2 smartforms site using Forms authentication
 

Diagnoses

The user receiving this error has a semi-colon in the password. This has been logged as a bug that has so far only been encountered when a semi-colon is placed in a user's password. If positioned in front or at the end, there is no error.
 

Resolution

Removing the semi-colon or placing it at the start or end will allow the user to login successfully