Java Security

hi to all, this is my first post.... sorry for my poor English :)

i have some problems while creating the secret key with DH.... the code below (the same in Server and Client) generating an InvalidKeyException from "doPhase".
i think this isn't a transmission error, Server and Client send and receive serialized object called "pacchetto" (the Italian word for "Packet").

(in the code below i simplified the "send" and "receive" but i think this is not the problem).

i want only to print out the result secret key

private void DiffieHellman(){

		String valuesInStr=genDHParams();
		String[] values = valuesInStr.split(",");
		BigInteger p = new BigInteger(values[0]);
		BigInteger g = new BigInteger(values[1]);
		int l = Integer.parseInt(values[2]);
		try {
			// Use the values to generate a key pair
			KeyPairGenerator keyGen = KeyPairGenerator.getInstance("DH");
			DHParameterSpec dhSpec = new DHParameterSpec(p, g, l);
			keyGen.initialize(dhSpec);
			KeyPair keypair = keyGen.generateKeyPair();

			// Get the generated public and private keys
			PrivateKey privateKey = keypair.getPrivate();
			PublicKey publicKey = keypair.getPublic();

			// Send the public key bytes to the other party...
			stream.writeObject(new Pacchetto(publicKey));

			// Retrieve the public key bytes of the other party
			Pacchetto pacchetto=(PublicKey)stream.readObject();
                        publicKey=pacchetto.publicKey;

			// Prepare to generate the secret key with the private key and public key of the other party
			KeyAgreement ka = KeyAgreement.getInstance("DH");
			ka.init(privateKey);
			ka.doPhase(publicKey, true);
			// Specify the type of key to generate;
			// see e458 Listing All Available Symmetric Key Generators
			String algorithm = "DES";

			// Generate the secret key
			SecretKey secretKey = ka.generateSecret(algorithm);

			// Use the secret key to encrypt/decrypt data;
			// see e462 Encrypting a String with DES
			System.out.println( "key: "+secretKey.toString());

		} 
		catch (InvalidKeyException e) {System.out.println(e.toString());} 
		catch (InvalidAlgorithmParameterException e) {System.out.println(e.toString());
		} catch (NoSuchAlgorithmException e) {System.out.println(e.toString());
		} catch (IOException ex){	System.out.println(ex.toString());
		} catch (ClassNotFoundException ex){System.out.println(ex.toString());
		}
	}
	private static String genDHParams() {
		try {
			// Create the parameter generator for a 1024-bit DH key pair
			AlgorithmParameterGenerator paramGen = AlgorithmParameterGenerator.getInstance("DH");
			paramGen.init(1024);

			// Generate the parameters
			AlgorithmParameters params = paramGen.generateParameters();
			DHParameterSpec dhSpec
			= (DHParameterSpec)params.getParameterSpec(DHParameterSpec.class);

			// Return the three values in a string
			return ""+dhSpec.getP()+","+dhSpec.getG()+","+dhSpec.getL();
		} catch (NoSuchAlgorithmException e) {
		} catch (InvalidParameterSpecException e) {
		}
		return null;
	}

the output is:

java.security.InvalidKeyException: Incompatible parameters