c# - C# trouble using bouncy castle libraries

Question

I'm attempting to encrypt something then decrypt it. The code shown below is VB but I'm using it with the C# libraries. I've tried the same code in C# as well with the exact same exception thrown.

I'm encrypting the text using the RSA engine and the private key file from a StreamReader. Writing that to the console works fine, but the invalid block length exception is thrown when I try to decrypt it:

Module Module1

    Sub Main()
        Dim input As String
        Dim output As String

        input = "Feb Twenty-Fourth Two Thousand Ten"
        output = EncryptKey(input)
        Console.WriteLine(DecryptKey(output) <---Error!

    End Sub

    Private Function EncryptKey(ByVal sPlain As String) As String
        Dim enc As New System.Text.UTF8Encoding
        Dim result As Byte()
        result = BouncyCastleCrypto(True, enc.GetBytes(sPlain))
        Return Convert.ToBase64String(result)
    End Function

    Private Function BouncyCastleCrypto(ByVal bForEncryption As Boolean, ByVal input As Byte()) As Byte()
        Dim bValue64 As Byte() = {0}
        Try
            Dim keypair As Greenway.PrimeResearch.Encryption.Crypto.AsymmetricCipherKeyPair
            Dim sr As New StreamReader("C:\Documents and Settings\xxxx\Desktop\test.KEY")
            keypair = New Greenway.PrimeResearch.Encryption.OpenSsl.PemReader(sr).ReadObject
            Dim cryptEngine As New Greenway.PrimeResearch.Encryption.Crypto.Encodings.Pkcs1Encoding(New Greenway.PrimeResearch.Encryption.Crypto.Engines.RsaEngine())
            cryptEngine.Init(bForEncryption, keypair.Private)
            bValue64 = cryptEngine.ProcessBlock(input, 0, input.Length)
        Catch ex As Exception
            Throw ex
        End Try

        Return bValue64
    End Function

    Private Function DecryptKey(ByVal sCipher As String) As String
        Dim enc As New System.Text.ASCIIEncoding
        Dim result As Byte()
        result = BouncyCastleCrypto(False, Convert.FromBase64String(sCipher))
        Return enc.GetString(result)
    End Function
End Module