Rudolf,
EG 4.22 and 4.2 custom tasks should be completely compatible. If you are having trouble getting a custom task to load when you think it should, please contact SAS Technical Support.
Hint: we built in quite a bit of behind-the-scenes logging for EG 4.1 and 4.2. You can enable the logging by following the instructions in:
http://support.sas.com/kb/17/730.html
Once enabled, you'll logging files appear for every EG instance that you run. They'll be located in "%appdata%\SAS\EnterpriseGuide\4.2\Logs" (where %appdata% is a system environment variable that resolves to your user profile area).
The process for loading custom tasks has lots of log messages: search the log files for the name of your task DLL for hints of what might be the problem.
Again, if you cannot resolve, please write it up for SAS Technical Support.
Chris