WHY there is a database error? help

I creat a process instance with c#.net code, but when i run it, the connection is good but an exception will be catch at "creat process instance", and error message is "An database error occured ."

Is something wrong? who can help me?

code :

System.Security.Principal.WindowsImpersonationContext impersonationContext;
impersonationContext = ((System.Security.Principal.WindowsIdentity)User.Identity).Impersonate();

SourceCode.K2ROM.Connection oK2Connection = UIController.NewOpenK2Connection();
SourceCode.K2ROM.ProcessInstance oNewProcessInstance;
oNewProcessInstance = oK2Connection.CreateProcessInstance("TrainingApproveTrainee");