Old projects like that one was originally made in MPLAB IDE. So you may find errors in the configuration of some of the new projects for MPLAB X. But that should be easily solved.
To clarify I think he means that many of those projects were for MPLAB 8 not MPLAB X. Going back to that might be a good starting point.
Also be aware of the compiler the demo was written for, this is have as much if not more impact on your success than the MPLAB version.
That said they should ALL work with a little fixing and tweaking but if you are very new to this environment and/or c programming in general it could be frustrating.
Don't forget you can post on microchip forums and submit support tickets with microchip. they will help you although they are sometimes slow.
Just like HERE though you must ask specific questions and provide a complete set of information. Saying you are having compilation problems doesn't leave anyone with any ability to help you beyond guessing. You posted some info but you need to complete it. What processor, which version of the solution libraries, what are the exact errors that are stumping you?