You could always take a look at the Logging module in the appstore, which stores the errors in your log file in your database. If they use a Java action, you could (ask to) reuse that one, otherwise, once the errors are in the database, you can access them regularly.
I would wait on Mendix 5. I can not yet reveil why, but it would be a waste of time if you start now.......
Regards,
Ronald