a fatal error occurred during run windows server backup in win srv 2008 r2

in windows server backup i want to backup but this error shown: unknown error 0x80042302 close wbadmin.msc and then restart it. i see event viewer, there are some error: 1- event id 8193 source vss 2- event id 13 source vss 3- event id 10 source wmi i search for several things and do them but can not repair it. in c:/windows/system32 the msxml3a.dll dose not exist. downloaded some version of it and try to register it by regsvr32 but it error "entry point cannot be found" thanks a lot