I have googled this error to death and can't figure out how to fix it. Hopefully someone can help!
I have roundcube installed on the same server as HMS (hMailServer). Everything works great and then all of a sudden "poof", roundcube won't let anyone login, it just throws:
"Connection to IMAP Server failed"
followed by:
IMAP Error in C:\Websites\webmail.mydomain.com\program\include\rcube_imap.php (142): Empty startup greeting (555.555.55.555:143)
Any ideas? If I reboot the server it all starts working again, but this sporadic IMAP issue is driving us nuts.