I tried to update my 536 and got the same error. I always clear the data and then update..this is the first time this has happened. Now we are all trying to figure this out.
Got it!
That would indicate that the SD card is likely corrupted (this can happen if the power is cut to the scanner during a write). You should be able to reformat the card, then use Sentinel's "Clear User Data" function, which will rewrite all necessary files. Then, Write to Scanner to put your settings/favorites lists back in.
I pulled out the SD card and put it into a adapter and followed the directions.