can you give us more info about the PE, like how many sections, what are their names, etc.

Also, look in the file with hex editor and see if you find any strings that might clue towards the protector.

Run the app in a debugger and see if it gives an error message. If so, what does it say and what does the message look like?

These are all indicators that can show the protector type.

The only protector I know of that will screw LordPE full dumps is Armadillo.

-Lunar