The Error 24 Could not write keep alive to comm sock
is caused because a socket was opened to communicate
with the client but was then lost or reset. You are
most likely either running out of available sockets 
when the problem occurs (which is why a reboot fixes
it) or there is a NIC issue that is causing socket
problems when this occurs. I would look at the
TcpTimedWaitDelay parameter in Windows to force the
sockets to close faster. By decreasing the
TimedWaitDelay parameter it forces sockets that are
not being used to close more quickly thus freeing up
the socket for use by NetBackup. You can verify if
this is the issue next time it happens by running a
netstat -a on the client. If you see a lot of
connections in a wait status then changing the
TcpTimedWaitDelay parameter will help.

Jeff Redington

"A wise man once said 'Wherever you go, there you are'"
      -Mike Brady