Error -1073807342 mostly is caused when the resource name passed to VISA Open is incorrect. Try to adress your device directly such as: GPIB0::5::INSTR. Make sure not changing GPIB adress on your target device ((Tektronix) while communicating with it.
As a precaution for error -1073807300 prove
following. Is there really only one session opened ?
If one of both errors occur, try to open a VISA session and communicate with your instrument via MAX (Measurement & Automation Explorer). Further try to reset your remote GPIB device.
How do you procedure when this error occurs ? Do you restart your VI which is responsible for communication ( or LabVIEW completly) ? Do you reset your GPIB device ? Do you restart your PC ?
Is this error dependent on your GPIB device (does this error also occur if you communicate with an other
instrument) ?
What GPIB Card you are using ?
Maybe you can attach your GPIB communication vi realized with VISA VI´s ?