VISA error code -1073807239

Hi,

I am using NI-VISA 5.4 to communicate with Keithley SMU 2636B. On the PC, my application registers a callback to receive service requests from the meter. Once a service request is received, the application calls "ReadStatusByte()" from the MessageBasedSession object to get the status byte and processes it.

That logic works fine most of the time. However, the call to "ReadStatusByte()" fails intermittently with the below error message:

"The protocol specified is invalid.  VISA error code -1073807239 (0xBFFF0079), ErrorInvalidProtocol"

I would appreciate any help I can get on this issue.

Thank you,