Hello Thomas,
When loading your ODF (either via 'Design tools | Load custom organ' or 'Design tools | Load organ (with design options)') you'll be shown the design options screen. Can you just confirm that you still get the crash with the 'Skip all organ definition validation for speed [caution]' option *not* ticked? (Organ definition validation is important to catch any ODF bugs that might exist during ODF development, otherwise an ODF bug could easily crash Hauptwerk.)
If that doesn't pinpoint the problem:
What audio editor (or other application) did you use last to save your release sample WAV files?
Are the release samples in separate WAV files from the attack/sustain samples?
If you temporarily substitute a release sample WAV file from another sample set that's know to work properly, does the crash still occur? (That might help to determine whether the problem is due to something in the relevant WAV files themselves, or something in the ODF.)