As Thomas said, check your rom (kickstart v37.299 (the worst) ? v37.300 ? v37.350 (good) ? v40.63 (vey good with a 600) ?) and workbench version.
If your rom is <3.1 (v40.68), try use other software than EasyAdf... or upgrade it (about 15 EUR for a 3.1 chip here in France).
