Fatal Error - 'Mongo' class not found
The problem was the PHP driver (php_mongo.dll). Apache/WAMP just did not like the mongo-1.1.4-php5.3vc6ts version for some reason. My Windows 7 Professional machine had the mongo-1.2.5-php5.3vc9ts version. That was the only difference between the two machines.
I originally had been using the mongo-1.2.5-php5.3vc9ts version of the driver on the Windows 7 Enterprise machine but changed to the mongo-1.1.4-php5.3vc6tsversion when I was troubleshooting the problem. So the original problem could actually just have been that the database path data\db didn't exist/couldn't be found (and needed to be specified using --dbpath when running/starting mongod.exe).
If this problem exist in php CLI you should add extension=mongo.so to your /etc/php5/cli/php.ini file
Check out the exact compiler name of your PHP binary in phpinfo page and try to reinstall the mongo driver was built on same compiler.
http://www.php.net/manual/en/mongo.installation.php#mongo.installation.windows
You're using the mongo driver was bulit on Visual Studio 6 with Thread-safe, now. ( vs6ts means it )
Similar problem was caused by compiler issue;