I think it might be memory related. The flight was going perfect until i got to my destination. I am flying a real world flight provided by deltava.org which is around 4000 miles (KATL-SBGL)

When I got to my destination i was trying to program my approach (RNAV 15 for example) and then my whole flight plan in the computer disappeared and i could not re-input the route again manually or by trying to load it.

After fiddling for a bit in the legs page i could finally get the FMS to take manually entered intersections and speed restrictions but the LNAV was still a bit clunky trying to follow the route.

Any ideas?