During Legacy Calendar or Legacy Mail synchronization, the following error is encountered.
RpcStoreAdmin::InitConnection Error -2147221231 ClassFactory cannot supply requested class : CExchAttendantCalls::ConnectEx failed! File: 'aeExchRpc.cpp' Line: '154'
RpcStoreAdmin::InitConnection Warning 1722 The RPC server is unavailable. Server name - AgentHost, service name - Quest Migration Attendant for Exchange service.
Assign full control over the Administrative mailbox, whether it be the System Attendant mailbox, or the one specified within Migration Manager as an Administrative mailbox.
Minimum/Granular permissions are acceptable, but need to be followed very carefully, as one missing step can cause this type of behavior of the product.
For more information on Granular Permissions, please see: