There’s no way for me to look at what permission scopes are associated with user IDs, so that unfortunately will not help.
Let’s take a step back. If you have not changed the permissions associated with your consumer key lately, then I can’t see what else might have caused this. Can you have one of the affected users try checking for your app (under twitter.com/settings/applications) and confirming that it shows “Permissions: Read, write, and direct message”? Can you also perhaps have them try revoking access and then re-authenticating? You’ll need to ensure you use the new access token to inherit the correct OAuth scopes.
