255 is the same error I had...look in your dive computer log for very short dives and delete them was the fix for mine. I had one 39 seconds which caused error 255. Once i manually deleted it from my Petrel, I could download all dives from it.
Ding! Ding! Ding! Ding!..... That was what it was. I got rid of all my dives less than 5 min & the other logs downloaded with no problems. Thank you!