imap_open() not working in RHEL4

Hi,
I have a stock RHEL4 server and not that the imap_open() function no
longer
works.
I have a local pop3 server running dovecot that I use to autenticate
with this line:
$imap_stream =
imap_open("{mailserver:995/pop3/notls/ssl/novalidate-cert}", $username,
$password, OP_HALFOPEN);

I get this error:
Warning: imap_open(): Couldn't open stream
{mailserver:995/pop3/notls/ssl/novalidate-cert}

I readed about and it seems to be GSSAPI configuration.

Anyone got imap_open() working on RHEL4/CentOS4?

Many thanks
Oliver