Hello, in Marketpress Version 3.2.1 when you create a coupon there is the option to apply it to all products, categories, products or users.
When you select one of the last three a new section shows up to, which I believe, is to select the category, product or user. But ours is blank.
I've attached a screen shot showing product selected, and the pop up blank.
Update - I notice there were a lot of script errors generated in Inspect Element and it references WPMU Dev's SEO.
I disabled SmartCrawl by WPMU Dev and it all worked.
You seem to have a conflict with the current version of Marketpress 3.2.1 and Smart Crawl 2.0