Cannot upgrade

Hi there,

Version 270.25 has been running great for some time, until today I tried to update to latest beta (354.28b1) when "firmware upgrade failed" sign appeared. Tried with latest stable (270.26b) with same result.

Any hints ? TIA

PS: first upgrade attempt was through wifi, following attemps were made through LAN cable, in case this is relevant
PS2: gee, just realized this was posted at the wrong forum, can any mod please move it to Merlin's firmware thread, please ?