IIS Handler Mappings changes order automatically

I have a web application running into a server and the Handler mappings in the IIS of it changes order automatically after some time showing the following error:

**Server Error in '/' Application.

Unable to validate data.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated 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. Information regarding the origin and location of the exception can be identified using the exception stack trace below.**

If I reorder the mappings into the IIS the web works again. Any idea about what could cause it? Is possible that the server restart cause the change?