Error E355: Startup failure
A published engine could not start. Possible reasons are modifications to the executable, resource, or script after publishing. This can also happen if the .CD folder contained old content. Delete the .CD folder and publish again.
you could try loading all of your levels in WED and saving and building them also you could load all of your old scripts in SED and save them too, this could work if the saving process has changed a little in A6.50...GOOD LUCK!