BTPS...
Had exactly the same thing happen with number listed in a seven day period (new seller) restriction last fall on Software. I could only list/revise about 10 items. If everything suddenly fails after you hit a number, that's probably a good candidate for reason.
I asked tech support, but also tried a direct listing. If you try to REVISE a listing on ebay in the group already listed and have a similar error, you have your answer too.
Danno