MySQL syntax error with PHP

I'm having a problem with MySQL 5.5.24 and PHP 5.4.3. I have the following HTML/PHP Code: ``` <?php function connect() { $con = mysql_connect( "127.0.0.1", "root", "" ); if ( !$con ) { die( "Could not connect: " . mysql_error() ); } mysql_select_db( "game" ); } function protect( $string ) { return mysql_real_escape_string( strip_tags( addslashes( $string ) ) ); } if ( isset( $_POST[ 'register' ] ) ) { connect(); $username = protect( $_POST[ 'username' ] ); $register = mysql_query( "SELECT 'id' FROM 'user' WHERE 'username'='$username'" ) or die( mysql_error() ); if ( mysql_num_rows( $register ) > 0 ) { echo "That username is already in use!"; } else { $ins = mysql_query( "INSERT INTO 'user' ('username') VALUES ('$username')" ) or die( mysql_error() ); echo "You have registered!"; } } ?> <form action="register.php" method="POST"> Username: <input type="text" name="username"/><br/> <input type="submit" name="register" value="Register"/> </form> ``` Whatever I input, MySQL will always return ``` "You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''user' WHERE 'username'='XXX'' at line 1" ``` I checked these queries with phpmyadmin and they work just fine! There is also no connection problem. I even tried plain `"SELECT * FROM 'user'"` with the same result. I simply do not get any response, just the mentioned error about malformed SQL syntax. Now I checked tons of articles having the same error and in each case the problem was having used a keyword of PHP or missing/mispelling a variable name and that kind. I checked my statements a hundred times now and I can't find any error. I'm quiet new to PHP so maybe I miss something... One of my last experiments was changing the collation of the database as well as the storage engine, also with no result... Hope you guys see what I can't! :-) BTW, I'm running Windows 7 and WAMP 2.2.