Error occurred while decoding OAEP padding

Hi,
I am half th way of my problem,,. Please Help
I have succesfuly encrypted the text using public key of digital signatures but while decrypting it. i am getting error
Error occurred while decoding OAEP padding
my piece of code
 
#region
Test Encryption
public void a()
{
using (var rsa = new RSACryptoServiceProvider())
{
// This String consists only Public Key Information
String publicKeyOnly = rsa.ToXmlString(false);
// This String consists both Private/Public Key information
String publicPrivate = rsa.ToXmlString(true);
}
}
//encrypt
public byte[] b(String publicKeyOnly)
{
String s = "<RSAKeyValue><Modulus>vi74tqVrIHSyFELPThmQHUmkZsPx+baueW1reayVWzUe1nT0mZCCqPOcCYKT25E5TLpAh/bMQReLGIvokK+EzzFPqT2Ka0oK0LgPgO2LGZECR4PHdW/UH+bSwWaxN4rikEQGEr0M7rVv5wBFxhcZ/EFv40im+MVIkiM7W2P8PTM=</Modulus><Exponent>AQAB</Exponent></RSAK ...