A few days into using the RTM release of Visual Studio 2010 I ran into a quirky bug with my aspx pages when flipping to design view.
Not all pages but on some I would get “The page has one or more <asp:Content> controls that do not correspond with <asp:ContentPlaceHolder> controls in the Master Page.”.
I spent a few minutes verifying that indeed my ContentPlaceHolder controls do match up. Not wanting to spend more time on it I ignored it because I don’t usually use design view for much anyways.
However, later I opened an aspx page and design view worked fine.. Hmm. So I then spent a few minutes to figure out the Visual Studio voodoo that made it work this time and fail before.
The difference is I had the actual MasterPage open in design view. Don’t ask me!
So as a “workaround” if you are experiencing this problem and it is not because you have your ContentPlaceHolder controls messed up open the MasterPage in design view first THEN open your aspx page and flip to design view.
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