This is due to the Post Cap in your Auctioning Operation being an invalid value, or set to 0.

A common mistake is setting this value to 0 in an attempt to set 'no limit' to how many items to post, where this will simply disable posting for that operation.

This field accepts custom strings, so ensure the resulting value is between 1 and 50,000 (Retail), or 1 and 200 (Classic).