Intermittent Access Denied for certain IDocs

Hello wM Gurus,

we are facing the following problem with the SAP Adapter 4.6 running on IS 6.5.

SAP system sends ZORDER_MODIFY idocs in to their RFC Queues and we have listeners configured. for certain Idocs, the Idocs are failing at SAP as they are receiving the Access Denied error. At the same time, the following error is logged in SAP Adapter logs

2008-08-07 12:30:17 BST [SAP.0006.0008W] Error in inbound call for IDOC_INBOUND_ASYNCHRONOUS from PROD: java.lang.RuntimeException: [ISS.0084.9004] Access Denied
IS errorlog:
pub.sap.transport.ALE:InboundProcess com.wm.app.b2b.server.AccessException: [ISS.0084.9004] Access Denied

I verified the /config/aclmap_sm.cnf file this has the following entry for the ZORDERMODIFY message,

SAPUsers
Anonymous
SAPUsers

These entries appear to be ok. our system is running in Produciton since 2 years and this is issue is seen newly.

Is anybody aware of this intermittent Access Denied errors? Is it a know error in SAP Adapter 4.6?

Thanks
Arjun