Right click on your icon file and click on Properties. Under the General tab, check to see if you have a Unblock button. If you do, then click on the Unblock button to unblock the icon file.
What type of drive is the G drive? As a test, save the icon file to a location on the C: drive (ex: Desktop) to see if it will work from this location instead. This will test to see if there may be a issue with it located on the G drive.
If you like, go ahead and upload your icon file in a ZIP file here, and I'll test it on my system to see if I may be able to spot anything wrong.