File post problem - ASP.Net

I have to a web services method called uploadFile.the method getting a parameter as base64str and record as a file into the specified address it. But,I have a problem.That method doesn't allow to upload more than 350 KB file.Otherwise,I can upload less than 300 KB file e.g zip, jpg, txt. Also, When I attempt to upload more than 350 KB file,a process working continually on server.

Process:

Image Name : w3wp.exe, UserName : ASP.Net v4.0, CPU : 50, Description : IIS Worker Process

Sometimes server cpu goes to 100%

Code:

  * encodedFile = Base64Str as format

    string postString = string.Format("userName={0}&userVendor={1}&vendorKey={2}&base64FileStr={3}&guid={4}&fileName={5}",                                 "kadi", "şifre", "key", encodedFile, guid, strFilename);


                string localHttpPostUrl = userGatewayAddress + "uploadFile";

                ASCIIEncoding encoding = new ASCIIEncoding();

                Stream newStream = null;

                HttpWebResponse response = null;

                Stream streamResponse = null;

                StreamReader streamRead = null;


               try

                {

                    HttpWebRequest request = (HttpWebRequest)WebRequest.Create(localHttpPostUrl);

                    request.ContentType = "application/x-www-form-urlencoded";

                    request.Method = "POST";



                    byte[] buffer = Encoding.UTF8.GetBytes(postString);

                    request.ContentLength = buffer.Length;


                    newStream = request.GetRequestStream();

                    newStream.Write(buffer, 0, buffer.Length);

                    newStream.Close();


                    response = (HttpWebResponse)request.GetResponse();

                    streamResponse = response.GetResponseStream();

                    streamRead = new StreamReader(streamResponse);


                    Char[] readBuffer = new Char[256];

                    ret = string.Empty;

                    int totalCharCount = 0; 

                    int count = streamRead.Read(readBuffer, 0, 256);

                    while (count > 0)

                    {

                        totalCharCount += count;

                        ret += new String(readBuffer);

        开发者_开发知识库                count = streamRead.Read(readBuffer, 0, 256);

                    }

                    ret = ret.Substring(0, totalCharCount);


                    return ret;

                }

                catch (Exception x)

                {

                    return x.Message;

                }

<system.web>
   <!-- 100 KB Max POST size -->
   <httpRuntime maxRequestLength="100"/>
</system.web>

http://support.microsoft.com/kb/832878