Hi Davu,
You MUST update in the correct sequence. First "All versions to 1.3.5." Next 1.3.5. to 1.4., then 1.4. to 1.5. and finally 1.5. to 1.5.5. If you do this in any sequence other than this you will find problems. It is quite logical really if you look at the link Mr. Robville gave you.
Angus.