VISA Write hangs after running OK for a while

Question

VISA Write function (VISA abc W) in my VI runs OK, with a Return Count of 4, for a while (100's to 1000's of times)  then it hangs.  The Return Count from this function is then 0.  The Error In and Error Out show no errors.  Clicking HIGHLIGHT EXECUTION shows the output wires from the VISA Write as colored grey, while everything else has normal color. 
Clicking the VI red ABORT button, or any of the sub VIs red ABORT buttons, fails to abort or reset the VI even after 20 minutes.  Task Manager will stop LabVIEW, but then LabVIEW will not start up again without shutting down and restarting the computer.  Changing to a different Windows XP computer and a different PCI-GPIB, NI-488.2  board, as well as reinstalling LabVIEW 7.0, or using a different LabVIEW 7.0 serial number, has not solved the problem. 
Thank you for your help.

Answer 1

Thanks for your reply.  Attached is a PowerPoint file that shows info on our computer and LabView, and a For Loop
(Slide 3) that runs the VIs addressing one of our instruments (Hart 1590 Super Thermometer).  Slide 4 shows the
block diagram that is pretty much as downloaded from National Instruments.  The block diagrams for each of the
colored sub VIs contains a sub VI having a VISA abc W function as shown in Slide 5.  The only places this VISA
function hangs is in inside the While Loop, inside the yellow Meas. Status. VI or the blue Read Meas. VI.  The
Meas. Status. VI sends "new", and  the Read Meas. VI sends "tem" to the Hart instrument. 
Also attaced are the VIs for the Measurement Status and the Read Measurement.  In the course of trying to fix this
problem I've added various time delays of 50, 100 msec, up to 1 sec, thinking that the Hart needed more time to
respond before receiving another command; none of this improved the situation.  I added indicators and arrays to
capture the last several strings that were input to the VISA function, but I saw nothing unusual.  All I've been
able to determine is that the VISA abc W function hangs as described in my posted message. 
Attachments:
VISA Write Hang 9-15-05.zip ‏282 KB