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Simply using another brand USB/232 adapter may help. Remember to uninstall the old drivers.
Personally I've not had the best of luck with the NI-Serial devices. The IOGear GUC232's have worked well for us for many years, and if you're looking to design a board with serial adapters on them, SILabs CP2102's play nicely with LabVIEW/VISA.
National Instruments does offer several USB-Serial options you can check out. As far as confidence goes, we have a wide base of users using these, and we'd be able to troubleshoot any further problems you have, although I doubt you'd continue to run into this problem. In the case of a BSOD for IRQ_NOT_LESS_OR_EQUAL, it's very likely not going to be your code or your Tektronix device causing the crash. I would definitely say your existing hardware and driver would have to be the prime suspect here.
I do not work for NI and as long as you do not buy it from me, I make nothing from NI USB-Serial adapters. That being said...
Any time I have the option to select the hardware, I use the NI version. They have worked flawlessly for me. If I ever did have trouble with them, I can talk to a human and not have to play e-mail troubleshooting tag. When an adapter failed (lightning strike) the new one installed as Comm 4 or something. A quick call to NI, and I found out the Serial drivers included a utility to let me change the Comm number assignments.
I had similar problems with a USB to serial device. A solution that worked for me was to change the VISA read/write VI's to synchronous. This setting is found by right-clicking on those VI's. Apparently this is a known issue with USBSER.sys. If you are using an IVI driver, then you may not have access to that setting in the VISA layer.