What expansions do you have, and is the game patched?
Did you delete the lot, or just everything inside of the lot?
Also can you attempt to place a new lot and zone it for community in "edit town" then custom build the park you want?
Have you already given the empty lot a function in Edit Town mode? With function I mean something like Community lot ---> Small Park for example.
Make sure anytime you do a new lot you choose the right lot size, and declare it as community lot and select visitors allowed.
Please reply and let me know how this works out, I love the sims 2 and somewhat tolerate 3.