well, I am not fully sure since you havent given us many details however, I havent used RSDlite in quite some time. I assume you have an xt912, and have the correct files to start with, and are getting the same error.
I would try and use Sam's House of Moto:
make sure you get all the correct files and read his instructions carefully.
for all flashing make sure to use USB2.0, the original Moto cable and have the latest drivers.