i also have 6600m and my updates went fine but that is not what you want to hear
let's see if i can help...
when you turn on the 6600M what sequence of colors did the power button go thru??
then we can check against the blinking light error set and figure out from here
note when down grading from 2.5.1 to 2.4.9 it is required to do a factory reset
you know the procedure for factory reset.
Hold power button until it start to blink white the let it go and see how it boots up.
Power Button Color Codes
The Power button is used to turn the radio on and off and is illuminated with a number of colors to indicate the radio’s operational state:
FLASHING GREEN: Radio is starting or shutting down
SOLID GREEN: Radio is in receive mode
FLASHING RED: See Error Conditions below
SOLID BRIGHT RED: Transmitting on PA
SOLID DIM RED: Transmit engaged, but transmit interlocks are not ready. Refer to the SmartSDR documentation for description of the transmit interlocks.
SOLID ORANGE: Transmitting on XVTR port with low power
SOLID PURPLE: Radio is performing a software update
FLASHING WHITE: Radio is performing a reset to factory defaults
OFF: Radio is off
Certain hardware and software error conditions cause the radio to stop operating and display an error code by flashing the Power button light as follows:
One red flash: Fan malfunction
Two red flashes: Software crash
Three red flashes: Boot failure
Four red flashes: Input power over voltage
Five red flashes: CPU overcurrent
Six red flashes: Input power under voltage
In the case of a software crash, the error code repeats for about 15 seconds, then the radio will reboot. In the other cases, the error code repeats until the Power button is pressed, then the radio shuts down. An additional press of the Power button is needed to restart the radio.
i know counting the number of flashes per sequence is not obvious
easy to do either
I have found that if I touch "Version" in the upper right I can go to the version selection window. If I select any of the versions loaded on the radio, it goes to the "Please wait..." window and then eventually shuts down. I am playing with that now. The typical sequence is for it to go through step 2..4 of the update sequence, then go to the "Please wait..." page, then shut down.
more likely software crash or boot error
this is the best info i can provide you...
if the factory reset and power disconnect does not clear the problem
i think Flex Help desk will get thru the problem..
i saw above that you did submit help desk ticket
sorry i could not have been more of a help
Just to let you know, your ticket is in and no one is near a computer that can actually work through this tonight. So sorry. We had many upgrades and down grades, so it is very possible a very unique event. I assume your initial upgrade was 2.4.9?
Anyway, we will jump on it in the morning.
Radio itself still fully operational from SmartSDR. I performed cols restart and factory reset but it does not recover from panel. During boot process front panel display shows Flexradio logo on black background followed by Welcome to Flexradio screen with blue background followed by blank screen. Radio part is fully operational from SmartSDR but I lost all setting trying recover front panel.
I then went into the menu and downloaded the new software and it loaded all 4 steps with no problems.. After playing around for 10 minutes I am calling it a night as I need to do a few things for the wife before bed time comes around.. OH, this was Software version 2.xx.xx.. If the reports on the most recent 3.xx.xx version are favorable, will go ahead and contribute my $200 to Flex and do the next update..
Not likely the case here but my only non boot issue was related to the network.