From: Morini on
Hi Jan,
 
It seems that there is another program which is using the serial port resource in the background. If that program/driver is loaded with windows, you will then get this error in Labview.
Can you tell me more about your system? What instrument are you trying to control, your operating system and your NI-VISA driver version?
 
You can try to update your NI-VISA to the most recent one: <a href="http://joule.ni.com/nidu/cds/view/p/id/988/lang/en" target="_blank">http://joule.ni.com/nidu/cds/view/p/id/988/lang/en</a>
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Please let me know if it helps.
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Thanks!