errcode=-4/-5/-6/-8 :
DATs do not contain required ARM7/ARM9 data to load the game. 
Also caused by outdated ttpatch.dat/r4patch.dat/m3patch.dat (file depends on which cart you are using).

errcode=-81/-82/-83 :
Caused by fragmentation on your µSD. Backup microSD to PC, then Full format with the Panasonic SD Formatter to rectify.

Any other error codes during loading, please refer to your carts website