This command is printed when all outlining regions in the file are already collapsed to definitions. For example, if you execute the command Collapse to Definitions twice, you will always get this message the second time. The same thing happens if you execute Expand All Definitions when all regions in the file are already expanded. One of the following things has happened.
The language service did not report any outlining regions in the file. In C#, this always occurs if the following option is not checked:
Tools → Options... → Text Editor → C# → Advanced → Enter outlining mode when files open
The Edit.StopOutlining command was executed (Edit → Outlining → Stop Outlining, or Ctrl+M, P).
All regions in the file are already collapsed.
You have identified a bug in the IDE, which you should report to Microsoft Connect.