Some add-ons are not written properly. When the Tracker tries to load them, they are failing in some way (perhaps they were written for an earlier release of the BeOS), and returning an error to the Tracker. The Tracker is only sharing the grief. :-
Other add-ons require extra installation steps, like modifying your "/boot/home/config/boot/UserBootscript" file. Be sure to read the add-on's documentation to make sure you've covered all the steps.
Contact the author of the add-on you're having problems with (hopefully their e-mail address is in the documentation for the add-on), and determine if you have the latest version. If you do, they may have more specific questions for you that can pin-point the problem.