I have the same problem with Win Svr 2k8 x64 and have tried everything I have seen posted. I get the "Unexpected error refreshing Server Manager: ... 0x800B0100)" error as well.
Here is the log from checking for system readiness:
================================= Checking System Update Readiness. Version 6.0.6001.22275 2009-09-09 14:11
Checking Deployment Packages
Checking Package Manifests and catalogs.
Checking package watchlist.
Checking component watchlist.
Checking packages. (f) CBS MUM Missing 0x00000002 servicing\packages\Package_for_KB955430_server_0~31bf3856ad364e35~amd64~~6.0.1.18005.mum (f) CBS MUM Missing 0x00000002 servicing\packages\Package_for_KB955430_server~31bf3856ad364e35~amd64~~6.0.1.18005.mum (f) CBS MUM Missing 0x00000002 servicing\packages\Package_for_KB955430~31bf3856ad364e35~amd64~~6.0.1.18005.mum
Checking component store
Checking SMI Store Summary: Milliseconds: 409921 Found 3 errors CBS MUM Missing Total Count: 3
I have tried to apply KB955430 for x64 Server 2008 but it will not take.