In my web application on aspx pages, the controls were not loaded, they had boxes on them with the error message.
Then I right clicked on my web project from the Visual Studio 2005. Selected the "Web" tab and put a tick on the radio button "Use IIS Web Server". then I clicked the button "Create Virtual Directory"
After I build the project, everything looked OK.
PS:Thanks a lot to Hosam Kamel, this problem had a solution really fast: