And since I will not allow simple file sharing on my LAN I have enabled the Guest account.
So when you disable Simple File Sharing, you are actually disabling the Guest account, so you would need to either re-enable the Guest account or Simple file Sharing for a Guest login.
I think you have misunderstood the security aspect here. Simple file sharing never increases security, but always decreases it, as it gives automatic read access to all shares regardless of the identity of the computer/account making the request. If you have a wireless LAN it might not even be a local computer at all, but some passerby outside with a laptop...
i would also recommend keeping Simple File Sharing enabled, because while it is enabled, ALL remote access to your PC MUST use the Guest account's permissions, which is read only and helps prevent any remote users from changing anything on your PC.