This error usually is the result of updates you have missed or installed only partially. To solve the problem, please install all updates checked by default at least, if not all. If you do not want to use the update function of Spybot-S&D, take a look at the download page here and download all manual updaters.
The cause of this problem are extensions to the detection engine which provide new ways of detecting malware. These updates are usually labeled Plugin, contrary to the weekly Detection update, and might therefore be overlooked. Since version 1.4 Spybot-S&D allows you to hide these messages, but this is generally not recommended since missing plugins might mean missing or reduced chances to find the latest malware.