ODEX 400 version 3.0 and above require OS/400 version 4.2 or above.
ODEX 400 versions below 3.0 will only work with OS/400 versions 4.5 and below.
This is due to IBM changing from using CPA threads to Kernel threads.
ODEX 400 was originally designed to use CPA threads but was changed to use Kernel threads from Odex version 3.0 onwards.