Problem with RSA when decrypting

[Elbarto]

Hi,

I am a newbie with cryptoPP

I am trying to decrypt a string that was crypted in RSA

but it doesn't work, I have an exception that say "Invalid ciphertext",

in my program the RSA private key was succesfully loaded, but when the 
program try to decrypt the ciphertext it doesn't work

I am sure that the ciphertext is Ok, so I don't understand, I need help 
please

here my source code:

 std::string Crypto::RSADecryptString( const char *privKey, const char 
*ciphertext){

        //privKey is the privateKey, in hexadecimal format
   StringSource privFile(privKey, true, new HexDecoder);
   RSAES_OAEP_SHA_Decryptor priv(privFile);

          //here we try to decrypt a ciphertext, here ciphertext is in 
hexadecimal format
        RandomPool randomPool;
   string result;
         StringSource(ciphertext, true, new HexDecoder(new 
PK_DecryptorFilter(randomPool, priv, new StringSink(result))));
   return result;

}

can you send me a source code who explain the encryption/decryption method 
for RSA ?

thanks