Dovecot broken, possible 'auth' problem.

[henry_h at fastmail.fm]

Hello,
  Something happened recently (possible Yum kernel update?) that has
  broken my Dovecot Imap. Service won't start, status says 'dovecot dead
  but subsys locked'. If I do a tail of maillog and try to start dovecot
  I see this when starting dovecot;

Jan 17 16:50:45 home dovecot: Auth process died too early - shutting
down
Jan 17 16:50:45 home dovecot: child 12831 (auth) returned error 127
Jan 17 16:50:45 home imap-login: fd_send(-1) failed: Broken pipe
Jan 17 16:50:45 home last message repeated 2 times
Jan 17 16:50:45 home pop3-login: fd_send(-1) failed: Broken pipe

Could something in a recent kernel update have broken things? Everything
was working fine up until 2 days ago. I'm using dovecot to run
Squirrelmail for multiple virtual hosts. 
Any help or suggestions appreciated.

Henry.