Cannot access ReadyNAS 214 after unit rebuild

I found  a damaged HD unit (12tb SATA) in my  ReadyNAS 214 (Firmware: 6.10.10 , RAID5). I Just replaced it with a new HD of same size, waited for the reconstruction of the NAS. Everything, apparently OK. But at the end of the process I cannot access the NAS by using my usual pw (nor with user:admin, pw:admin). I'm redirected to a page for the password recovery. I answered to my recovery question, but the page hangs! Tried with a different PCs (win10, win 7, etc.) and different browsers (Chrome, Edge). No changes. A PC is still connected to the NAS as shared disk, and from it I can see alla the files of the NAS. But recovering the password is apparently impossible via browser, also from this pc!

Any help?

Cheers