SpamAssassin score missing?

[Max Kipness]

Hi,
 
I've been getting a lot of messages (spam) this morning that have no
spam score. Some messages when looking the headers this morning do have:
 
X-MailScanner-SpamCheck: not spam, SpamAssassin (score=0.5, required 8,
HTML_80_90 0.50)
 
But some just have:
 
X-MailScanner-SpamCheck:
 
With nothing after the colon. Does this mean SpamAssassin is timing out?
I see no indication of any problem in the mail logs. 
 
How can I fix?
 
Thanks,
Max