[CentOS] NFS problems with CentOS 4.5

Our large and complex build system is having very sporadic failurs
as we try to update to CentOS 4.5.  This takes the form of files that
exist - and have existed for some time - not being found:

file.whatever: No such file: No such file or directory

This happens both with source files, .o's - meaning that the
errors come from both the compiler and linker.

The build storage is on NFS and the errors don't happen when we target
local disk.  We also have solaris nad Centos 3.x building the same code
base in a similar fashion with no problem.

We are currently using mount options of:
rw,nosuid,bg,timeo=50,retry=1
And have also tried:
rw,intr,bg,proto=tcp,nfsvers=3,rsize=32768,wsize=32768
without success.

Any suggestions welcome.

-Mark