I just did an in-place upgrade from 17.3 to 18.3 (because I heard there was an issue with Mint19 and older Core 2 Duo machines). My old Lenovo Idea Center K210 tower ran 17.3 perfectly with a Linksys USB wireless adapter. The in-place upgrade seems to have carried all my settings properly, but when I try to connect to my router, it rejects the password. I've verified the password is correct but it still continues to ask for the proper password. I've deleted the connection, rebooted the router, and tried to connect afresh, but it just won't accept the correct passphrase. I'm still a noob and need some help on where to proceed.

After quadruple checking everything, found transcription error in passphrase. Must have been entered during one of the rebuild attempts. Still doesn't explain why initial logon attempt failed, as it should have carried forward intact during upgrade. All other remembered passwords were working fine.