Encrypt and decrypt data accessible by multiple users within a team
One potential risk is your AES key length. Using a key length of 64 bits or less is not advisable as it can be relatively easy to brute force these days. Recommend that you use at least 128 bits. 

As for your problem when a user is removed, you may like to try something similar to PGP. Each time you commit a file to the server, you encrypt it with a randomly generated symmetric key and encrypt the key with the public keys of all other legitimate users. In this way, a removed user would no longer be able to access newer files. 

But I dunno if that will be secure enough, its two cents worth.