Which SQL Server product does version 622 represent?
622 is an internal intermediate version, never released. How come you have an 622 version DB? The explanation is simple actually: an aborted upgrade. Look at the sequence Aaron posted:

Converting database 'x' from version 611 to the current version 655. 
Database 'x' running the upgrade step from version 611 to version 621. 
Database 'x' running the upgrade step from version 621 to version 622. 
Database 'x' running the upgrade step from version 622 to version 625.


If the last step above crashes, your database is a version 622 now (each step commits). This version can only be attached to a SQL Server 2008 (or newer) to continue and finish the upgrade. It seems to me you had a SQL Server 2005 DB (v. 611) you attached to a SQL Server 2008 or higher, it started to upgrade but the upgrade failed at step 622->625 and now you're trying to attach it back to the SQL 2005 instance. It can't be re-attached, your only chance is to try to move forward. If the upgrade continue to fail, you will have to start again from an original SQL 2005 database (a copy of the files, a backup...).

Why would a database upgrade fail? Same reason any operation can fail: CTRL-C, power outage, corrupted original database, hardware problems, bugs in the product. Knowing what the upgrade step 622-625 does, my moneys are on a corrupted source DB. Recovering from a failed upgrade is a bit more tricky. As usual, having a good, tested, backup and restore strategy pays off.