Is this new, and has this problem existed since your first cook? Is your vent at least partially open? If moisture backs up into the generator it can cause it to short out. Make sure the inside of the generator is dry, and there is no debris built up.
There could be a few reasons, but tracking down the cause can be tricky. First make sure you have the correct size fuse. The fuse size should be 10A 250V. If the fuse size is correct, unplug the tower from the generator and then turn on the generator. If the fuse doesn't blow, you know the problem is in the tower. If it blows, it is likely that you have a short, or an overload or incorrect wiring in the generator. Make sure there is no debris that cause a short between terminals. Another possible cause could be a faulty bisquette burner, they have been known to trip GIF's and/or fuses.
If you are still under warranty give Bradley a call.