Forwarding doesn't work: 'No valid agent found for search string US <userID>'

[Kouw, FA - SPLTX]

Hi,
 
Can someone help me out with the following:
 
When I try to forward a work item to another user I get the following
error on production (not on acceptance...):
 
   * No valid agent found for search string US <userID>
 
I forward the work item in the following way:
 
   * select the work item in the inbox
   * select button 'forward'
   * select button 'possible users' (in dialog box 'Choose agent')
   * double click on a user in the list
   * select button 'continue (enter)'
 
Forwarding of a work item is no problem in case it concerns a general
task. The work item that causes the problem has a selected group of
users assigned as possible agents (thus not a general task).
 
All help appreciated!
 
Regards,
 
Fred Kouw
 
 
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