@roocket
Even though you've supplied some basic device info, unfortunately saying "File from post #28 does not work" is not enough to guide us to give proper advice.

Your nuvi 255W must have HWID of 0827 to have any chance of converting to 465T (without BT). If it has HWID 1091 the conversion cannot work. If you've tried to flash an RGN named "082701000xxx" to a 1091 device, by design Updater.exe will refuse to do so for safety.

Only if it is a HWID 0827 device: Please supply more, and detailed, information on the problems encountered. Give details of the board version also:
  • Hold battery symbol for ~6 seconds to enter a hidden menu - then post the device's details following 'Version Information' shown at the top of the first page.
  • On the next page (press lower right hand corner to page), note and advise the PCB P/N details shown immediately below 'Version Information' there.

Include screenshots of any errors given by Updater.exe if available.