Ive come across the same problem at a number of customer sites recently, so I thought this might be something worth posting about.
The problem typically comes about as customers who’ve traditionally had vCenter running on a 32bit Operating System, now move to a x64bit Operating System to support vCenter 4.1 which enforces x64 bit architecture.
Now the actual root cause of the problem is the NetWorker 64bit client does not have the necessary nsrvim binary which is responsable for communicating with vCenter.
The good news is the fix is actually very simple, within the properties of the vCenter server youve configured in the NetWorker Management Console, just change the command host to any other networker system running a 32bit version of the client ( 7.5 and above ).
Typically the command host and the end point field have the same server configured, but as you can see from the screenshot below Ive just changed this to one of my test clients named “Client1”
Save the changes and away it goes again. Hope this helps.