What is in Measurement and Automation code?

[momof4]

Hello, We have a program that uses GPIB communication to talk to 2 devices.  We have LabVIEW 2009 and use VISA vi's.  For some reason, an error occurs while the program is running at random points during the test.  When this happens, we are unable to run the program until we run scan for instruments in Measurement & Automation.  What is Measurement & Automation doing that clears the GPIB error?  Any advice would be greatly appreciated!

THANKS!

[momof4]

.....more info.  I am communicating with a Ruska 6660 and a Schwien Pressure Standard both fairly old devices.  The failure occurs intermittently but I will try to post a screen shot of the error when or if it occurs.  THANKS!

[Albert.Geven]

For old instruments try to set the bus speed to 2microseconds in the gpib propertiesin MAX.

This sometimes helps.