note 108668 rejected from function.mcrypt-encrypt by danbrown

Note Submitter: anupamchakma at gmail dot com ---- below is my encryption function, it is working well with php5.3 but when i try to use the same in php5.1, it doesnt work the program terminates before encrypting...Its neither giving a syntax error while compiling...please suggest where i am going wrong..... function encrypt($string) { //Key $key = "xxxxxxxx"; //Encryption $cipher_alg = MCRYPT_DES; //MCRYPT_TRIPLEDES; $iv = mcrypt_create_iv(mcrypt_get_iv_size($cipher_alg,MCRYPT_MODE_ECB), MCRYPT_RAND); $encrypted_string = mcrypt_encrypt($cipher_alg, $key, $string, MCRYPT_MODE_ECB, $iv); return base64_encode($encrypted_string); return $encrypted_string; }