Error at loading Project

Question

Hi, I have created one ASP.Net Project, in which I have created 3 webforms. I have used the codebehind approach and 2 webforms are linked with the 2 codebehind class written in C#. Now the problem is, when I open the project or when I double click the .aspx file, I get the following error message: "The file failed to load in the web form designer. Please correct the following error, then load it again: Visual Studio cannot open a designer for the file because the class within it does not inherit from a class that can be visually designed." After responding this error message box, the project opens perfectly but all code characters are now in black, the "blue" color is disappear and quick list is also disappear. When I remove the "Inherits" and "Src" attributes and then save, close and re-open the file. Everything gets fine. Plz help me, I am not familiar with this. I am waiting for your reply.