What can I do to resolve the issue whereby, the permissions of all users suddenly change even for the admin, I cant access any other modules.
I have never encountered this issue before. Did something go wrong when you were saving permissions? If this is the case, you can empty the database table gibbonPermission, and then copy and paste the gibbonPermissions from gibbon.sql in your Gibbon root. You can find the part you need to copy and paste by searching for: