Hello,
First, you need to attach the subVI's as well in order to take a look at the code in any detail; if you can do this I'll take a look! Second, if you can give a more detailed description of your problem it will make helping more efficient. In particular, you noted that communication using VISA and SCPI commands works... does this give you your desired functionality. Which resource of port are you communicating through (Serial, GPIB, etc.)? Does the HP driver you refer to use HP VISA? Are you have a problem with a dll call as the others in the stream you posted to discuss?
I won't ask further questions now, but any and all information about your system will likely provide insight into the solution!
Thank you,
Best Regards,
JLS