Simple news - Undefined Variable Error?
Clear your cache completely. Disable your current them and enable a core theme like Garland. If the error goes away, you'll know it's with your theme. 

If not:


Was the database fully migrated? 
Were your files (and theme!) fully
migrated?
When you say "standard" block.tpl.php file, where did it
come from? It should have come from /modules/block/block.tpl.php.