I am also having problems like these with SR245. I did have the interface working perfect under Windows XP SP1/Labview 6.1. Since returning to use it now, I initially had GPIB Write errors.
On upgrading NI VISA and NI 448.2 drivers to latest versions (3.4 and 2.5) I seem to be able to write to SR245 (notably with different termination characters than previously!), but get no replies.
Checking on NI Spy shows no specific errors, only the waiting for a reply that doesn't come (I set a long timeout).
One further nail is that I had downloaded and used the SR245 GPIB Labview driver (available on the developer zone site). I remember this working well in the past, but now it suffers from the same communication problems.
This all seems to me to be some sort of driver (VISA?) issue, possibly related to Windows XP-SP2?