System.Web.HttpException: Unable to validate data

unable to validate data. Description:An unhandled exception occurred during the execution of the current WEB request. Check the stack trace for more information about the error and where the error occurred in the code.

Exception Details:System.Web.HttpException: Unable to validate data.

Source Error:

An unhandled exception was generated during the execution of the current WEB request. You can use the following exception stack trace to determine information about the cause of the exception and where it occurred.

Stack trace:

[HttpException (0x80004005): Cannot validate data. ] System.Web.Configuration.MachineKey.GetDecodedData (byte[] buf, byte[] modifier, Int32 start, Int32 length, int32& DATALENGTH) +195 System.Web.UI.LosFormatter.Deserialize (String input) +60 [HttpException (0x80004005): Authentication of ViewState failed. 1) If This is a cluster, edit <machineKey> configuration so all servers use the same validationkey and validation al Gorithm. AutoGenerate cannot is used in a cluster. 2) Viewstate can only be posted the same page. 3) The ViewState for this page might is corrupted.] System.Web.UI.LosFormatter.Deserialize (String input) +118 System.Web.UI.Page.LoadPageStateFromPersistenceMedium () +101 [HttpException (0x80004005): invalid_viewstate Client ip:127.0.0.1 port:1893 user-agent:mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.2;. NET CLR 1.1.4322) viewstate:ddwxody1njiynza4o3q8o2w8atwwpjs+o2w8ddw7bdxppdexpjtppdezpjs+o2w8ddx0pdtwpgw8atwwpjs+ o2w8cdzlhazlj7jlhoxpg6jlhazmlofkv53lr4y75yws5y+45yaf6yoo5yws5pah5l+d5a+gpjs+pjs+ozs+ o3q8ddw7cdxspgk8md47pjtspha85pmu6ycao+azrumamj47pj47pjs7pjs+pjs+pjs+vqqb2s1cqu9rlhoi9o607b+p3x4= Http-referer: Path:/attachcs/upload.aspx.] System.Web.UI.Page.LoadPageStateFromPersistenceMedium () +447 System.Web.UI.Page.LoadPageViewState () +18 System.Web.UI.Page.ProcessRequestMain () +447

Workaround: Set the Prohibit MAC (authentication code) in the page directive: <% @ Page enableviewstatemac= "false" >   view state Message authentication Code (MAC) is an authentication token (also called Checksum, the code is created when both the authentication scheme and the key are applied to the message. The MAC is calculated and validated by using the same key. Therefore, the MAC can only be validated by a predetermined receiver. You can use a variety of encryption techniques and algorithms to create Macs, such as the Secure Hashing algorithm (SHA), the Message Digest 5 (MD5) algorithm, or the Data Encryption Standard (DES) algorithm. The

View state MAC feature is used to prevent customers from sending requests that contain malicious view state data. By default, the view State MAC feature is enabled by using the enableviewstatemac= "true" flag in the Machine.config file.

To determine if the problem you are experiencing is related to a MAC, the easiest way to do this is to turn off the feature. To do this, set the enable VIEWSTATEMAC flag to False . If you no longer experience view-state errors, the issue is related to the MAC.