pawolf98, could you share which report(s) you're trying and include which option(s) you're selecting? A few reports aren't able to be exported (and the Export button is grey and inactive) until you make a specific selection. For example, the "Issues checklist" needs to have at least one of "Issues of each title" or "Missing issues of each title" selected before anything can happen.
And not that it probably matters a whole lot, but note that you posted this in the Atomic Avenue technical issues forum. It's better housed in the ComicBase technical issues forum.