Hello

As first: I have not installed a 2.anything version of mlf.

1. i upload all 2.0 stable and install clearly.

So you should have a new, clear installation.

2. i log into PhpMyadmin and select all tables and empty all tables.

If you empty all tables, you clear the table(s?) with the forums settings too.

3. i import my old sql bak to the new mlf database.

If there are any changes in the structure of the database tables the outcome may be an error. I don't know wich version you used before (it seems to be the beta 26?) so look as first into the changelog and follow all version steps between your last used (the beta) and your actual installed (the release) version.

Then it's over,when i check my index page's soucecode,there said

<meta name="generator" content="my little forum 2.0 beta 26" />

No HTML document head, only this source code fragment?

The template enginge seems to get the information about the version from the database (exactly: from your restored backup) but lacks some other informations to build the complete HTML source code.

It may be a solution to delete (inclusive the database; you have the backup) and reinstall the actual release. Then control the backup of your old forum (again: changelog). Maybe you need to adapt the stored SQL structure of the backup files (make a backup of the backup before ). As last restore only the postings and user related tables into the new database but not the software related tables.

Tschö, Auge