Vcentre 4.1 is not supported with Avamar SP2 there are some known issues with it as the vSphere API has changed and its not compatible.
Vcentre 4.1 will be supported with Avamar 5 SP3
What is the link to the Avamar 5 SP3 Download?
What version of Proxy / Is there a specific link for the Proxy Servers for vStorageAPI usage?
You need to contact AvamarSupport and have them install it for you as a part of your support agreement. It should only take about 4 hours to complete.
I dont believe the proxy server changes from previous versions of Avamar. It has relied on VMWare's API which changed between 4.0 and 4.1.