If you search the forum for "Include errors.log", you'll find 66 discussions from other people who asked what this message means. Here's a screenshot of what I refer to:
There is on option on the settings page, called
Ignore if single detections in include files need a newer program version.
which would make this message go away if checked, but otherwise, it should show up on each scan, probably multiple times.
Are you sure you haven't seen this during scans?
And since you said you upgraded quite often, take a look at the updates that all versions of Spybot-S&D download (warning, tech talk ahead):
http://www.safer-networking.org/updates/spybotsd.ini
It's a bit technical, but in the group
[Main update 1.5.2], there is
no MinBuild parameter, meaning that it will show to all versions up to the
MaxBuild one, which here is 20071230 (1.5.2 itself). Both the "Importance=Hoch" and the exclamation mark in front of the "Info" field tell the update function to pre-check this update in the list of updates Spybot-S&D shows. So, from the technical perspective, everything looks quite like 1.3 would show the main update.
That is theory alone of course and quite technical maybe, so I went ahead, took a fresh 1.3, searched for updates, and voila:
The main application update shows, and installs when clicking the download button. Unless you right-clicked the entry and told Spybot-S&D to ignore this update, it would show up again and again. And if you stopped the update after starting it, the setup file to install the new version should still remain visible on your desktop.
Between 1.3 and 1.4, I have to admit there might not have been a full installer, just a message that told you to download the newer version, which is no longer reproducible today, so I can't retest that condition.