I had been working for a client with a contract in place, and the contract stipulated that I could not be held liable for damages or lost profit. After the contract had expired, I mistakenly continued to work on the project, even sending an invoice.
After the contract was expired, the work was, of course, considered late. Considering the client and I had no active contract during that time, can I be held liable for any lost profit for the late work?
What does your original contract say?
Terms in your original contract might apply - I have conditions in my contracts that state along these terms (roughly saying that unless otherwise agreed the terms of the contract continue for six months after end of contract or until both sides agree in writing).
Your client is more likely at fault than you are - Your expired contract explictly said you are not held responsible for losses so they would face an up hill struggle to think those conditions changed.
Are they sueing you? Are they refusing payment? See if you can find compromise, if not, seek advice from a lawyer.
(and consider editing your OP and stating what part of the world you are in).
If you are on a time-and-materials basis, then work done after any expiration date is implicitly assumed to be done under the same terms as any work performed before the expiration date. If that's the case, the work done was lawful, the invoice was lawful, and the expectation of payment is lawful.
If the contract is for time-and-materials, then a due-date for delivering work product is invalid if the client has had any ability to modify the requirements during the contract term.
All this would be different under a fixed-price agreement, but you didn't state.
