Why adding a researcher to a project through Association key fails in some cases?

The first FCT public keys included the login followed by 4 characters from the password. This was a security risk which caused the forceful expiration of these keys. The researcher should access https://sig.fct.pt/fctsig submit his/her login credentials and will find the Association Key following the Login menu item.
In case the login credentials are unavailable, they should be recovered using https://sig.fct.pt/fctsig/preregisto.asp?action=esqueceu which requires reintroducing the email used for registration. The system will automatically send a login and password reminder.