The OpsMgr event log on the RMS showed many times Event ID 31569 with these details: ‘… Report deployment process failed to request management pack list from SQL RS Server. The operation will be retried.
Exception 'WebException': The request failed with HTTP status 407: Proxy Authentication Required (The ISA Server requires authorization to fulfill the request. Access to the Web Proxy filter is denied. )…’
It turned out there had been a change of proxy server several months ago and was enforced to all users by a GPO. Even though the SCOM 2007 R2 service accounts had internet access, the Data Warehouse WRITE account needed additional adjustments as well.
Case closed !