DM 800 flashing problem

I am trying to flash my Dm800 Original with a new image via network. It currently has Blackhole V12. I power off the box and and power in back on with the power button held in to get the ip address to enter into my browser. When I enter the ip address into my browser I get into the Dm800 web interface and it allows me to select an image to flash. I select the openatv image which is nfi format as required and it brings the file onto the web interface ready for flashing.
When I then hit the flash button nothing happens. I have tried various browsers....internet explorer, chrome and firefox but it gets to the same stage each time and wont flash when I hot the flash button. Has anyone any ideas what could be wrong?

Just tried with firewall turned off....same result :-(