Check to make sure you have all fields filled in i.e. Price, Zip Code, Address, Shipping, Returns, Handling. Check each item that is required to be filled in. Make sure you didn't use words in your title that would be rejected by ebay. Like the word "Free".
Seems like you should be getting an error code that clearly identifies what is missing.
One other thing, have you been listing continuously through Auctiva or have you been gone and just started again?
Go to your Saved Listing and scroll down to the bottom where it says Preview, Estimate Ebay Fees, and then Error Check. Click Error Check and see if it tells you.
Don't know if any of that will help but if you have missed any fields it could produce that error. Good luck.