AsyncFileUpload file size limit

Question

When I was using AsyncFileUpload to upload 100KB image, I got no error message, but image not uploaded. I can upload 75KB image succssfully. I am using IIS 6.0.

    <cc1:AsyncFileUpload ID="afuImg" Width="400px" runat="server" 
UploaderStyle="Traditional" ThrobberID="Throbber2"  
    OnClientUploadError="uploadErrorImg" 
    OnClientUploadStarted="StartUploadImg" 
    OnClientUploadComplete="UploadCompleteImg" />

<httpRuntime maxRequestLength = "1024000" 
executionTimeout="54000" 
enableHeaderChecking ="false" />