Really, Symantec says it's supported? Because it is NOT. NO version of 5.1 on a master is supported any more. You've reached end of life and end of support. You should contact whoever told you it's supported and ask them how to make it work and how to get support for it.
First, there's a clear differentiation in the support documents between support for the desktop product and the server product.
According to the 5.x compatibility list, 5.1 supported SLES 10 with no service packs identified.
According to the 6.x compatibility list, 6.0 supported SLES 10 with no service packs and you need a minimum of 6.0MP3 for SP1.
There is no version of SLED 10 supported with any version of NetBackup today. The highest supported version for the SuSe Desktop is 9.3.
5.x:
ftp://exftpp.symantec.com/pub/support/products/NetBackup_Enterprise_Server/263839.pdf6.x:
ftp://exftpp.symantec.com/pub/support/products/NetBackup_Enterprise_Server/278064.pdf