Symptoms

 When we tried to deployed K2 project below error appear.

"Notification Service: Task Error: System.InvalidCastException: Unable to cast object of type 'System.DBNull' to type 'System.Bytey]'."

also when we tried to deployed old version or tried to deploy other projects the same error appear.
 

Diagnoses

a cold fix is present to resolve the issue
 

Resolution 

Issue resolved after applying a coldfix.  Please contact K2 Support to request this coldfix.