What category are you listing in?
I understand that some categories such as trading cards and comic books no longer support a "--" as an option for Condition item-specific; if you are using that, try changing to "new" or "used" depending on what options are available in that category. And make sure any other required item-specifics are valid.
More details here:
https://community.ebay.com/t5/Share-eBay-Technical-Issues/It-looks-like-there-s-a-problem-with-this-...
