Hi everybody,
Problem fixed. I've Changed the following in $RCDIR/plugins/managesieve/lib/Net/Sieve.php
var $supportedAuthMethods=array('DIGEST-MD5', 'CRAM-MD5', 'EXTERNAL', 'PLAIN' , 'LOGIN');
Changed to:
var $supportedAuthMethods=array( 'PLAIN' , 'LOGIN');
Thanks you,
Werner