E2740 (NI EDVR) DOS Error is perhaps the most common error experienced by MET/CAL users. This error indicates a mismatch between the number of IEEE-488 boards installed or plugged in to your computer and the number configured in MET/CAL.
The first troubleshooting step is to check the number of boards in your computer. You can do this in the NI Measurement and Automation eXplorer (MAX).
If you have only one IEEE-488 board, it must be named GPIB0 or MET/CAL will not recognize it. Right click and select rename to change the name to GPIB0 if necessary.
If you have two IEEE-488 boards, they must be named GPIB0 (all standards used during calibration must be connected to this bus) and GPIB1 (the Device Under Test (DUT) must be connected to this bus). Any other named IEEE-488 boards are ignored by MET/CAL and can cause the error mentioned.
Once these settings are correct, you can change your MET/CAL Configuration to match the number of boards in NI MAX. Up to version 8.3 of MET/CAL, this was done through the Configure>IEEE-488 Boards menu option.
In MET/CAL version 9.0 and up, this is done in the Configure>Instrument Control section of the MET/CAL Configuration.
These steps will resolve the E2740 Error.