Symptoms

Workflow errors out when it gets to Create Mailbox for User.
I am testing the workflow and I got the following error when the workflow tried to create a mailbox for a user:
Create Mailbox For User
Message: Exception has been thrown by the target of an invocation. Cached credentials for K2Service] could not be found. You can cache credentials via the "User Settings": "Single Sign-On" area in K2 Workspace. ServiceName: Exchange Administration ServiceGuid: 55627c31-e7f0-41f7-8ef6-d916f8284e68 InnerExceptionMessage:
 

Diagnoses

The issue was caused by Logon Name property of this account is not set as FQN (missing "@domain.xxx").
 

Resolution

After correcting the property of this account in AD, the process was able to create mailbox for this account successfully.