During simulation, Multisim creates a temporary file which is saved to the C:\ drive which contains the actual simulation output. This is the file that Multisim is having difficulty finding. This file path is set by environment variables. If you are in a situation where you do not have write access to your C drive (since you are installed on your G:\) drive I would recommend changing your environment variables with the following procedure:
1.) Start >>Control Panel >> System
2.) Click on the "Advanced" tab
3.) Click on the "Environment Variables" button
4.) Change the TEMP and TMP environment variables to point to a place where you have write access, such as on the G drive.