( System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent ) in explicit interface declaration is not a member of interface

 hi
i have an error in this code, can anyone fix it for me pleas.
 
The error is :
 
Compilation Error
Description: An error occurred during the compilation of a resource required to service this request. Please review the following specific error details and modify your source code appropriately.

Compiler Error Message: CS0539: 'System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent' in explicit interface declaration is not a member of interface

Source Error:

 

Line 28:   // Implement the code that will run
Line 29:   //  when called from the client.
Line 30:   string System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent(string argFromClient)
Line 31:   {
Line 32:     return GetAddress(argFromClient);
 

Source File: c:\AppDev\ASP20EXP\CS\Post ...