Publishing new product in MarketPress: Connection gets reset by server

I have a local fresh test install WP 3.5 Multisite, plugin Marketpress 2.8, theme Framemarket 1.4.9.6.
After putting in the settings for marketpress I can create new products. When I click "publish", then the product gets saved, but it will not show again in edit mode - the browser says "The connection was reset by the server "