If you are using a flash uploader to upload files with a progress bar to your .NET application and getting IO Error #2038 you may be hitting the 4MB upload limit on the file uploader. <system.web><httpRuntime maxRequestLength="2097151" executionTimeout="3600"></httpRuntime></system.web>
IIS 7 requires a second setting to go above 29MB: <system.webServer><security><requestFiltering><requestLimits maxAllowedContentLength="209715200"></requestLimits></requestFiltering></security></system.webServer>