When I open my project written on VS2005, one of my *.vcproj file cannot be opened with this error message.
The message says there are duplicated attributes in the *.vcproj file. To solve the problem, open the file *.vcproj file in a text editor, such as Notepad or Wordpad, and find the specified lines.
There may be something like this :
Remove one of them and save *.vcproj file.
I'm not sure why this happens, but it may be a bug in VS2005. Maybe, it does not occur on VS 2008.