type 3 error is an 'illegal instruction' error, unless Apple has changed that error number designation in OS 9. (are you using the OS 9 GM?) so it ostensibly means that there is perhaps a compatibility issue but maybe...
i do have an idea: try giving your troublesome app's a bit more RAM... maybe a meg or two. more in the case of netscape, if you can spare the RAM give netscape 18-22Megs or more even...
won't hurt, could help. OS 9 is too new for me yet, i have not run even a beta of it so i am guessing here, but MacOS 8.6 was giving trouble to some, i think it was type 2 errors and the recommendation was to increase the RAM allocation to the 'problem' app's... who knows, try it.