welcome to the site,, 1st thing i would do is try to replicate the error your getting. does it do the same thing while hooked upto shore power? if not take the tester rod talked about and try it on the generator and confirm if that is proper. then move onto other items, tying to isolate the problem.
another thing to consider is if the generator is sufficient to provide enough constant power. some items, such as a battery charger have delicate boards to them, and do not like fluctuating power being supplied to them.
personally i would return the coleman and get a honda generator. i went through 3 of the colemans from home depot over a summer of weakfishing off 7bridges.
