I copied standard BSFN B4100910 to custom B5841009 and made some mods to it. It works fine on client and builds successfully.
The standard BSFN has DLL COPBASE, where as for the custom, I changed it to CCUSTOM. But it started failing on the server. I have checked the code and the mods are not too much, or out of sync that would cause BSFN to fail on server.
After this i changed the custom BSFNs DLL back to COPBASE, but still it fails on server.