I wanted to sell something on Ebay again after years, but my selling limit has been set to 0 items and €0.When I apply for a limit increase, I only get an error message.

Hmm, you've racked up quite a lot of red ratings with this account for non-delivery, @samantha@ebay could it be that this account was temporarily or even permanently suspended from selling?*ahem... then that should probably also apply to the other account.