Symptoms
We they were experiencing was an issue whereby two of their users could not submit a request via SmartForms to start a K2 workflow.
Worklist item could not be opened. Unable to cast object of type 'System.String' to type 'SourceCode.Workflow.Client.User'.
This only happens on a SmartForms Client event. Studio and K2 for Visual Studio worked fine
Diagnoses
It seems the issue is limited to SmartForms Client events and can only occur if the user that started the process has managed Users. (ie is the manager to some users in AD) and the Workflow server is set to use Managed Worklist.
Resolution
It seems the issue is limited to SmartForms Client events and can only occur if the user that started the process has managed Users. (ie is the manager to some users in AD) and the Workflow server is set to use Managed Worklist.
The Managed Worklist must be disabled to have this issue resolved
http://help.k2.com/onlinehelp/k2blackpearl/userguide/4.6.7/webframe.html_reference_-_workspace_-_managed_users.html
