Anish,
If the characteristics are changing depending on what cards are installed, it sounds as if there may be some timing issues that are occuring. It is possible with the second card is installed the increased usage of the PCMCIA slots causes slower response of the GPIB bus and instruments. This could cause a problem if the program encounters a timeout while waiting for an event to occur (read,write,srq...). You could try opening your program and manually increasing the timeout settings in your vi to allow more time for a response.
Also, you mentioned that these were device specific drivers, are these from our web page or a third party? You could download the driver for the HP8753 from our webpage at the following address:
http://zone.ni.com/idnet97.nsf/9b2b33e1993d87778
6256436006ec498/99fd4a9bfc561ba7862568ab005fbb48?OpenDocument
You may want to check if your current driver has write and read functions dependent on events such as the instrument raising the SRQ. If so, try replacing these with typical write and read functions.
Another troubleshooting technique is to run execution highlighting (the light bulb on the toolbar). With this on, you can slow down and follow the execution to see exactly where the error is being produced in the program. Once you work down to the specific calls that cause the error, it will be much easier to find a reolution.
Best Regards,
Chris D
