VISA 5.2 Serial problems on Windows XP

[RTSLVU]

I have a test that is using two Agilent 34904 data loggers connected through RS232 serial.

LabView 2012 12.0f3(32bit) VISA 5.2

The LabView program will run fine for a few minutes to several hours, but eventually it will stop with a VISA timeout error.

If I then open MAX and try to connect to either of the data loggers with the VISA test panel and do a basic *IDN? query MAX locks up on "Attempting VISA write"

I have to reboot the computer for VISA to be able to operate on either com port.

I have tried different data loggers and a different computer but still the exact problem happens.

I have included my code, I know this is not my best work but it was thrown together rather quickly...

[RTSLVU]

I wrote the last post in a hurry yesterday and have a few clarifications...

The units are Agilent 34970A DAQ/Switch units. I have been using these for over a decade so I am fairly confident it is not a configuration issue or a problem with the 34970A's

I am not even sure where to go next as I have rebuilt the program several times, removed and reinstalled the LabView and VISA runtimes on the target machine, tried different 34970A's (we probably have 50 of these in the company), even different serial cables.

Any suggestions would be greatly appreceated.

[mikeporter]

Is this a built-in serial port or a USB dongle?

Mike...

[RTSLVU]

They are on USB to Serial dongles, they are Prolific dongles that again I have been using for years and have had no previous issues with. I have them on a powered USB (2.0) hub too, because not enough juice from the USB port was my first thought

[mikeporter]

Can you send and receive commands with another program like hyperterminal?

Mike...

[RTSLVU]

Once the program "crashes" I can not as Hyperterm says the ports are in use.

Both ports still show up in the Windows Device Manager and in NI-MAX

NI-MAX VISA test pannel locks up when attempting any writes to either port.

The command return display shows "Attempting VISA write on Com (X)"

[RTSLVU]

I may have this fixed....

When I installed the USB to Serial dongles the Prolific website was not responding so I downloaded Prolific drivers from Cnet.

Today I managed to get to Prolific.tw and downloaded the drivers from them.

I have several hours running without a problem....

We will see if it makes it through the weekend.