FuzzMeasure cannot recognize a license key file unless it has the .fumekey3 file extension.
Some email programs will add the .xml extension, which does not allow FuzzMeasure to recognize this as a valid file to open. Other email programs will strip the extension altogether, so you have to add it.
To solve this problem, either remove the extra .xml extension, or add the .fumekey3 extension, depending on your particular situation.
