nfs tranfers hang in state getblck or nfsread

I'm running an nfs server from a freebsd 4.8 box and accessing in from a 
5.1 client machine. On small transfers I usually have no problems but 
when I run a high bandwidth task (normalizing audio tracks) the 
normalize process often gets stuck in the getblck state or nfsread 
state. The priority on this process is also set to -1.  Has anybody else 
experienced this problem? Thanks for the input.