I've never really understood Window's network file sharing security model very well. Every time I end up trying to get it to work, I either set up an account that explicitly has every access right possible, and then put those credentials in the client's keychain, or do like you have, and try to remove all possible access restrictions.

If I recall, there are permissions both for the filesystem, as well as for who has access to the share. I want to say share permissions are checked first, and file permissions second, however, I could be wrong.

If you're getting access denied messages, maybe try to check out the event log on the serving machine to see what user it thinks is accessing the files. That should at least be a start.