RSA problem - "Unspecified Error"

I am trying to encrypt and decrypt data using RSA.  Ultimately, I need to be able to place an existing public key into the RSACryptoServiceProvider and encrypt using that, but for now, I'd settle for any success at all. 

I have this simple test.  I assure you that the LoadFromFile() and SaveToFile() methods are working, and the raw data is a valid byte array with the correct data in it.  The line (as indicated below) which encrypts data throws an exception, stating "unspecified error".

I get this behavior on two machines (Windows XP Pro SP2 and Windows XP Home SP2), but not on a third machine (Windows 2000 Pro).  What must I do to get it working?

Any ideas are welcome.


private void button2_Click(object sender, EventArgs e)
{
// Load the raw data to be encrypted.
byte[] lOriginal = LoadFromFile(@"c:\firstfile.txt");

// Create an encryptor with new keys
RSACryptoServiceProvider lRSA = new RSACryptoServiceProvider();

// Encrypt the raw data.
//This line throws CryptographicException: "Unspecified Error"
byte[] lEncrypted = lRSA.Encrypt(lOriginal, false);

// Store the encrypted data.
SaveTofile(@"c:\encrypted.txt", lEncrypted);
}