Pkg exim4 users - Aug 2008 - X-SPF-Guess: failed to expand ACL message

Hello,

on Debian Etch with Exim4 I sometimes have this error in the paniclog :
failed to expand ACL message "X-SPF-Guess: ${run{/usr/bin/spfquery --ip 
\"$sender_host_address\" --mail-from \"$sender_address\" \
--helo
\"$sender_helo_name\" --guess true}{pass}{${if eq 
{$runrc}{2}{softfail}{${if eq {$runrc}{3}{neutral}{${if eq 
{$runrc}{4}{unknown}{${if eq {$runrc}{6}{none}{error}}}}}}}}}}": command 
timed out

(I enabled the "Debian''s SPF checking" by adding
"CHECK_RCPT_SPF = true"
in the configuration.)

Is it just a problem due to DNS timeout, or is it a "configuration 
problem" ?

If it''s a DNS timeout, is it "normal" that this throw an
error in the
"paniclog" ?

Can I avoid the "command timed out", by reducing the timeout in 
/etc/resolv.conf for example ?
Or maybe increase an "Exim command timeout" ?

Thanks,
Olivier