If you're using stored procedures and mysql_error() returns "PROCEDURE storedProcedureName can't return a result set in the given context", you need to pass an additional flag (CLIENT_MULTI_RESULTS) to mysql_connect() as such:
mysql_connect($hostname, $username, $password, true, 131072);
Some other sources say that you should use 65536. 65536 is actually the flag to allow multiple statements in a single mysql_query(), and is a security issue. The reason it allows you to receive results from stored procedures is because it implies 131072. To be safe, use 131072 over 65536.