Unable to use existing keys in RSA Cryptoservice provider class

Question

I need to use RSA encryption in my wp8 app and send it to the server. But the trouble I am facing is that I know the public key of the server and I need to encrypt the data in app side using the key. But as far I infer from all the posting here, RSACryptoservice provider class doesn't support a key from another source(Am I wrong?). Is there any way to use the class in such a scenario? Or can this be done by using third party library only?

I tried the following function but still no use. What am I doing wrong here?

public static string RSAEncrypt(string data)
{
    try
    {       
        //initialze the byte arrays to the public key information. 
        string  pk = "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQD0cNKUgLdLMpW5BWB+PAlIIIiqhSXk66PQVemUnRs3nowRcBETfUkMIfDcPDM1FXhh+/2FqsnFLveCYl980bylZlBghkjUleknV4dGLfQPuLE7oxk4tbQF6Zk9Fmc9ynxvZ7XDuLmdn/4mdxW7BmcSomLIxkkGHynKkkXk5QcKQIDAQAB";

        byte[] PublicKey = Convert.FromBase64String(pk);
        //byte[] Exponent = { 1, 0, 1 }; 

        UnicodeEncoding pi = new UnicodeEncoding();

        //Values to store encrypted symmetric keys. 
        byte[] dataBytes = pi.GetBytes(data);

        //Create a new instance of RSACryptoServiceProvider.
        RSACryptoServiceProvider RSA = new RSACryptoServiceProvider();

        //Create a new instance of RSAParameters.
        RSAParameters RSAKeyInfow = new RSAParameters();

        //Set RSAKeyInfo to the public key values. 
        RSAKeyInfow.Modulus = PublicKey;
        // RSAKeyInfow.Exponent = Exponent;

        //Import key parameters into RSA.
        RSA.ImportParameters(RSAKeyInfow);

        var rslt = RSA.Encrypt(dataBytes, false);
        System.Diagnostics.Debug.WriteLine(rslt);

        return Convert.ToBase64String(rslt);
    }
    catch
    {
        return null;
    }
}

Am calling this function in another page as:

private void Button_Click(object sender, RoutedEventArgs e)
{
    var myString = "this is my string data";

    var x = Class1.RSAEncrypt(myString);
    MessageBox.Show(x);
}

The error I get is "Value cannot be null. Parameter name: messageBoxText"

I think the problem here is not passing the exponent, but I don't know how.