Strange problem about resolving role

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Hi all, 

I get a strange problem and have no idea. 
I created a workflow triggered by the changed event of BUS2032. The approval steps should be like below: 
accountant -> manager -> product manager -> general manager 
accountants and managers are from subordinate companies, so I created new roles using responsitibility, and make salesorganization in the salesorder as the role container element, It really works perfect. So I created another role to resolve product manager, which should be identified by division (VBAK-SPART), but now it doesn't work, it just send to everyone defined in the role responsibilities!! 
I tested through PFAC_DIS and it really returned the correct person. When I checked "Terminate if role resolution has no result" in PFAC, it raised a runtime exception WL 423 saying "Workflow no. 3032 step 32: Error or exception resolving role 'AC90000006'". But when I restart the workflow using SWPR, the role resolution runs successful, as we expected, only the proper product manager receives the work item. 

So could anyone of you pls give me a clue how to solve the problem? Thanks in advance for any help. 

BTW:
My system is 4.6C with support package KB46C48

regards, 
tiger