When I start FS I keep getting this error message," FS cannot find the aircraft for the requested flight. The default will now try to load." This started lastnight. My aircraft is the Cessna 172. I saved and made my default an airport that I train out of (KMLJ).

I even resaved it with no change.  Any ideas?

Heya Galactic_Eyes,

Bill is correct, however, in my experience when you get that error message when FS 2004 is loading the flight it means that something is wrong with the aircraft.

Two things to check:

1.  Open your Main FS 2004 folder.  Open the Aircraft folder.  Make sure that the default Cessna 172 folder is still there.  It's simply titled c172.  If the folder is still there, open it and look inside.  There should be an Aircraft.cfg  file, an *.air file and a Model folder for this Cessna.  If any of these are missing then you'll have to get them back.  The procedure for Extracting default aircraft from the FS 2004 Install CD is not too difficult.

2.  The *.FLT or *.WX file that is used to save the flight may be corrupted.  You may need to go to the main FS 2004 screen, delete this flight, then re-create it.

Now according to your post, you said that you re-saved this flight and there was no change.  When you deleted the bad flight from the FS 2004 main window and  Re-created the new Flight, did the default Cessna 172 aircraft picture appear in the selection screen OK?

I assume that it did, however, your post didn't say.
I for one will be happy to help out if you need further help.