Razor-Report: Signature not being produced

For the past few days when I submit my "Not Detected As Spam" emails
to razor-report the process completes very quickly and every email
says "Engine (8) didn't product a signature for mail x".

Log
------------------------------------------------
Apr 12 09:53:32.370241 report[77188]: [ 6] Engine (8) didn't produce a
signature for mail 16.0
Apr 12 09:53:32.370508 report[77188]: [ 6] computing sigs for mail
16.1, len 2652
Apr 12 09:53:32.374546 report[77188]: [ 6] Engine (8) didn't produce a
signature for mail 16.1
Apr 12 09:53:32.374863 report[77188]: [ 6] computing sigs for mail
16.2, len 10374
Apr 12 09:53:32.382114 report[77188]: [ 6] Engine (8) didn't produce a
signature for mail 16.2

I have run this on the same emails, and different ones but the same
always seems to appear.

Is there a reason for all emails to not get a sig. returned?

Thanks, PaulG.

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