I looked all through this forum and everywhere esle for several hours. No luck. I tried some things that might not be the right thing to do but in the end I got something to work.
When yum updates it must change the Virtuamin configuration for PAM. There is a proftp config file in /etc/pam.d (called 'proftp)with some pam config options I added another file called ‘ftp’ (just ftp ) with these options without removing the other file -proftp.
auth required pam_unix.so nullok
account required pam_unix.so
session required pam_unix.so