[Dovecot] started with dovecot sieve

[mailinglist]

As I am new to dovecot and sieve I am really happy to get it working in 
a straight forward way. Thanks for the documentation to whom it 
concerns.

Now I came to my limits with this failure messages in 
/home/rolf/.dovecot.sieve.log:

sieve: info: started log at Jun 25 20:22:54.
error: 
msgid=<1340648569.94073.YahooMailClassic at web190304.mail.sg3.yahoo.com>: 
failed to store into mailbox 'INBOX': BUG: Unknown internal error.

with this messages in mail.info:

Jun 25 20:22:54 rolf14 postfix/smtpd[21674]: connect from 
localhost[127.0.0.1]
Jun 25 20:22:54 rolf14 postfix/smtpd[21674]: 90898E0190: 
client=localhost[127.0.0.1]
Jun 25 20:22:54 rolf14 postfix/cleanup[21669]: 90898E0190: 
message-id=<1340648569.94073.YahooMailClassic at web190304.mail.sg3.yahoo.com>
Jun 25 20:22:54 rolf14 postfix/qmgr[21172]: 90898E0190: 
from=<stephanie.otavy at live.com>, size=5291, nrcpt=1 (queue active)
Jun 25 20:22:54 rolf14 postfix/smtpd[21674]: disconnect from 
localhost[127.0.0.1]
Jun 25 20:22:54 rolf14 dovecot: lda(rolf): Error: setegid(privileged) 
failed: Operation not permitted
Jun 25 20:22:54 rolf14 dovecot: lda(rolf): Error: sieve: 
msgid=<1340648569.94073.YahooMailClassic at web190304.mail.sg3.yahoo.com>: 
failed to store into mailbox 'INBOX': BUG: Unknown internal error
Jun 25 20:22:54 rolf14 dovecot: lda(rolf): Error: sieve: script 
/home/rolf/.dovecot.sieve failed with unsuccessful implicit keep (user 
logfile /home/rolf/.dovecot.sieve.log may reveal additional details)

I guess the mentioned mail is spam. However, does this tell about some 
wrong configuration or access rights? Any indication what to improve? I 
get such an error about every 6 minutes.