Downgraded MySQL from 5 to 4.1, now problems

If you saved backups of version 5, you can recreate the accounts which should convert over without trouble. Atleast that worked for me when a client requested a downgrade.

you could also try
/scripts/mysqlup --force

 

Since you downgraded MySQL without taking a full dump and then restore of databases, this is very likely to happen. The error message is self-explanatory.

If you have a backup, dump the database, and then restore it into 4.1.x.

It is a very good idea, before MySQL upgrade/downgrade, is to have backups, to be on the safe side.

If you go to: http://dev.mysql.com/doc/refman/5.0/en/downgrading.html at the bottom of the page, you'll read:

"These steps are given in The normal symptom of a downward-incompatible table format change when you downgrade is that you can't open tables. In that case, use the following procedure:

1- Stop the older MySQL server that you are downgrading to.

2- Restart the newer MySQL server you are downgrading from.

3- Dump any tables that were inaccessible to the older server by using mysqldump to create a dump file.

4- Stop the newer MySQL server and restart the older one.

5- Reload the dump file into the older server. Your tables should be accessible.