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Thank you Rolf, for your reply! It would make sense, that Windows permits applications to access VISA driver ports. Especially for Vista, since Vista uses stricter communication policies than XP. But does somebody know how enable other applications instances to talk to an opened session? Is there some kind of switch in the Windows Vista registry or something similar? By the way, what's the option "Duplicate session" in the VISA Open VI for? Thanks in advance for your answers.

Hello all, I have a problem with VISA when trying to access an already opened session. I get the following error: VISA:(Hex 0xBFFF0072) The resource is valid, but VISA cannot currently access it. (error code 1073807246) I know from several other discussions, that this error may occur if I try to access an opened session. For example I want to communicate with one device with two individual applications. To make sure, that only one application talks to the device, I use the VISA Lock/Unlock. And the thing with the two applications works for me with our USB device, if I use Windows XP, no matter what Labview or VISA version I use. I tried Labview 2009 and some 8.x versions in combination with VISA 4.4 and 4.3. It works all the time. Having installed Vista on the same computer, it doesn't work. I get the mentioned error everytime, no matter what I do!! Does someone know how solve this problem? I also want this working on Vista (and in time also on Windows 7, but haven't tried that, yet). An does someone know what's the purpose of the VISA Lock/Unlock, if a VISA session can only be accessed by one application? Best regards