I just wanted to report a problem I encountered. When changing from one server to another, I used phpbb's back up feature to create a database file. When restoring on the new server, (1) I got a "selected file to backup is invalid" message. This is a known issue that is fixed by correcting line 219 in /includes/acp/acp_database.php. With that fixed, (2) I proceeded to restore the database but was unsuccessful. From what I could tell, most of the basic table structure was in place but only a small fraction of content was filled into the tables, and user information was completely absent. To work around this, on the command line I ran `mysql -u -p dbname < dbfile.sql` (using the same file but uncompressed) and so far everything appears good. My conclusion is the backup worked correctly but restore has issues.

I hope this helps.