Footballer go to select aircraft. Under the manufacturer type pick 'Any', then the next row down there will be the aircraft type, click on the little triangle to the right of that and scroll through the list to see if you can find it, it might be the plane comes up under something unusual.

my suggestion would be to print the flight plan out & check it for typo erros such as missed commas or spacing errors. It might take a while but this way is better than trying to do it on screen as you should get the entire line for each flight.
In most cases it is a missed or extra comma that causes this problem. & this is the only way I can think of to find them. 8)