I'm too busy at the moment to provide expedited support for pay, but here are some things to check out:
- Does the login_redirect table exist? If not, you might have to manually create it with the SQL contained in the plugin file.
- Do any other redirect rules save? If so, there might be an issue specifically with the update function for "all other users"
- Does your configured database user have the permission to edit fields in all tables in the WP database? Perhaps for some reason they don't have valid permissions for the plugin tables.
- Are you trying to redirect to a URL outside of your install? Check the $rul_local_only setting
- If you're only setting a single redirect for all users, you could bypass the database entirely by hard-coding your URL in the redirect_wrapper function in the plugin