Re: upgraded X-Cart 4.x does not work with X-Payments (it won't work!)
OK, so after tons of messages posted (including PMs on this forum) it seems that we are close to finding the reason of the trouble.
And it looks like eBay integration module installed in this X-Cart somehow prevents right connection between X-Cart and X-Payments. Also, there were some left-overs after upgrade.
VP of Business Development for X-Cart