Error 30559 when using CWVisa1.ReadAysnc

[JasonAtSeagate]

I have a simple applicaton that talks to an instrument using the Visa control. The communication works ok from the Test panel within the Visa properties dialog, but fails in the program. I call Visa.OPEN, then Visa.Write commandstring, but Visa.ReadAsync fails with Error 30559, "Unable to queue the asynchronous operation"

[JohnM 64]

Hi Jason,

This is actually a driver error that occurs when using asynchronous reads and writes with Measurement Studio 6 and NI-VISA 3.0. The driver generates that error because the asynchronous operation you called could not be queued. ComponentWorks for Measurement Studio 6 enables both the event queue and the handler for the same event type on the same session. VISA 3.0 and later does not support that functionality, and you should only use it with Measurement Studio 7 or later.

To verify if this is actually the error that is occurring, you can try an example program that uses these calls to eliminate any possibility of other programming issues. The example programs using either ReadAsync or WriteAsync should also generate this error. You can also use the NI-Spy utility to catch the error. This utility should show error 0xBFFF003B (VI_ERROR_QUEUE_ERROR) Unable to queue the asynchronous operation.

To correct this issue, there are basically two options: upgrade to Measurement Studio 7, or uninstall NI-VISA 3.0 and reinstall NI-VISA 2.6.

Have a great day.

John M
Applications Engineer

[Y3G]

Hi John,
Well your advise will be my last hope... You can read/follow my hopeless trials at http://forums.ni.com/ni/board/message?board.id=170&message.id=128070.
It started with another error and basically was all the time Error 0xBFFF003B.
Where can I download Measurement Studio 7?
Best Regards
Yariv

[Y3G]

Thanks John,
It worked after I replaced VISA 3.1. with Visa 2.6.1

2 days of investigations ...