warnings in mail.warn

[Hans]

Within the /var/log/mail.warn i found the following warnings:
warning: redirecting the request to postfix-owned data_directory /var/lib/postfix
warning: request to update table btree:/var/spool/postfix/smtp_scache in non-postfix directory /var/spool/postfix

What do these warnings mean and how can this be solved?

(This is a Debian Lenny server with ISPConfig2)

[falko]

I've never seen such warnings before...
Did you modify your main.cf?
Do you use Maildir or mbox? What's the output of

df -h

?