MYSQL - INSERT error, unknown column in field list

try this (enclose each variable inside query with single quota):

mysql_query("INSERT INTO accounts(currentbalance, balancein, category, notes) 
          VALUES ('$balancenew', '$difference', '$category', '$notes')");  

Its better to use mysqli or PDO to prevent from SQL injection attack, you could use mysql_real_escape_string() for now:

$balancenew = mysql_real_escape_string($balancenew);

and for other variables.