This is a problem happed when you specially have upgraded from SharePoint 2007 to SharePoint 2010.
The problem is the page cannot be opened and we cannot change the layout. So here is solution.
Go to the site/page where the problem appear, in the link bar add this link /_layouts/viewlsts.asp after site link.
Click on site actions – site settings – Page layout and site templates – Make sure the page layout is here. Just in case everything fine here, click Ok.
Now let’s change the page layout:
- Go to Site Content and Structure
- Find the Pages library
- Find the Pages
- View Properties of the page
- Edit item
- Choose a valid page layout
The problem should be solved.