Hello John -
It sounds like you need to add the required Custom Item Specifics to your listing - please be aware that eBay is requiring such information in more categories as time passes, so items that may not have had such a requirement previously may do so as these changes occur. You can add the Custom Item Specifics on the lister page when you are working on your listings. For the categories where this is required or available, after you select your category the link for Custom Item Specifics is just below the Item Condition Note field. Just click the link and any of the fields noted with a green * are required by eBay for that category.
Once you have added the required information, you should be able to post your listing.
If you continue to encounter difficulty, please file a support case from under the Help tab of the site letting us know the trouble you're running into and an example listing or two where this is occurring and we'll be happy to look into this further.