It really doesn't make sense that you can do it in 10 and not 11. Those versions are extremely similar and there were no changes to my knowledge that would have any effect on this.
Using Filemaker 11:
Can you use Manage | Layouts to switch layouts? (I know this opens the layout in a new window, but this is a test.)
If you double click a few of these layouts in the Manage Layouts window, is the "include in layouts menu" check box selected?
If you don't spot any issues that way, try recovering the file. Even if FileMaker reports that no problems were found, test the recovered copy to see if you have the same problem.
Things to keep in mind about Recover:
While Recover almost always detects and fully corrects any problems with your file...
- The recovered copy may behave differently even if recover reports "no problems found".
- Recover does not detect all problems
- Recover doesn't always fix all problems correctly
- Best Practice is to never put a recovered copy back into regular use or development. Instead, replace the damaged file with an undamaged back up copy if this is at all possible. You may have to save a clone of the back up copy and import all data from your recovered copy to get a working copy with the most up to date information possible.
And here's a knowledgebase article that you may find useful: What to do when your file is corrupt (KB5421).