[exim] Problems with TLS and my certificate / private key

Hi!

I'm trying to use TLS with Exim 4.60. I'm using a pair certificate/private
key from my bussiness' PKI. I use these certificates without problems in
Apache, Courier, ... But with Exim I'm getting this error in logs if the
client use TLS to send messages:

2007-07-26 09:35:15 TLS error on connection from ([XXX.XXX.XXX.XXX])
[XXX.XXX.XXX.XXX] (SSL_CTX_use_PrivateKey_file file=/etc/exim4/exim.key):
error:0906406D:PEM routines:PEM_def_callback:problems getting password

Both certificate and private key file are in PEM format, encrypted with
RSA1 and 1024 bits.

I use these lines to configure TLS in exim.conf:

tls_certificate = /etc/exim4/exim.crt
tls_privatekey = /etc/exim4/exim.key
tls_advertise_hosts = *

A client with TLS see:

[user@host mydir]# telnet YYY.YYY.YYY.YYY 25
Trying YYY.YYY.YYY.YYY...
Connected to YYY.YYY.YYY.YYY (YYY.YYY.YYY.YYY).
Escape character is '^]'.
220 Mail System
ehlo test
250-host.mailsystem.com Hello test [XXX.XXX.XXX.XXX]
250-SIZE
250-PIPELINING
250-AUTH LOGIN
250-STARTTLS
250 HELP
starttls
454 TLS currently unavailable
quit
221 host.mailsystem.com closing connection
Connection closed by foreign host.

What can be the problem with the private key or certificate files?

Thanks!