Strange exception. Invalid archive type when execute an action

Dear all,

 I get the exception when I try to execute an action in a WorklistItem.

Dim wli as WorklistItem = conn.OpenWorklistItem(SN)

wli.Actions("ActionName").Exectue()

I run this code no problem in my dev environment. But when I move it to production, it doesn't work and gives me that exception. What does it mean? What are the possible reasons?

 Please help. Thanks very much.

 
-Kel