ASP.NET

Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded.
i am getting this error after uploaded my application on server. The same application works fine on local.i have used vs 2010,asp.net for the same

Private Function UploadToFTP(ByVal fileToUpload As HttpPostedFile) As Boolean

Try
Dim uploadUrl As String = "ftp://........................."
Dim uploadFileName As String = fileToUpload.FileName

Dim streamObj As Stream = fileToUpload.InputStream
Dim buffer As [Byte]() = New [Byte](fileToUpload.ContentLength - 1) {}
streamObj.Read(buffer, 0, buffer.Length)
streamObj.Close()
streamObj = Nothing

Dim ftpUrl As String = String.Format("{0}/{1}", uploadUrl, uploadFileName)
Dim requestObj As FtpWebRequest = TryCast(FtpWebRequest.Create(ftpUrl), FtpWebRequest)
requestObj.Method = WebRequestMethods.Ftp.UploadFile
requestObj.Credentials = New NetworkCredential("UserID", "Password")
Dim requestStream As Stream = requestObj.GetRequestStream()
requestStream.Write(buffer, 0, buffer.Length)
requestStream.Flush()
requestStream.Close()
requestObj = Nothing

Return True
Catch ex As Exception
Return False
End Try
End Function