Hi there,
There is a 60-day trial license for the Sharepoint agent (as with any other agent). 60 days after "installing" it, it expires and you won't be able to backup Sharepoint.
If you have it installed, push out the RAWS agent to the Sharepoint server and try again.
if it still doesn't work, post the error here for further investigation.
Here is a tech article to read up on too...
http://seer.entsupport.symantec.com/docs/340858.htm
Laters!