Thank you DPieron for this suggestion I am going to try next!
but until now I experienced something I could not explain:
I had the same problem and tried to FORMAT THE PRS 505 drive. I was able to, I even checked the drive was blank, then tried to reinstall Sony update,(18040) still did not let me.
I reformated again and while the drive was empty I removed the 505 from the USB just to check if it was working..... like the phoenix raising from its ashes, the menu was still there lake before despite full formating !!!! nothing had changed,
still with the 25200 version. is that spooky or WHAT? I am puzzeled.