TOk, so, I flashed my M900 with one of the 6.5 ROMs currently floating around on the internet, and to be quite honest, I was disappointed.

So I tried to go back to one of the 6.1 ROMs but literally every ROM I tired either gave me the 'SDMMC Load Fail' or 'OS image is NOT compatible with this hardware' error messages. I tried everything, reformatting as FAT with 64k block size, renaming the .bin file, the multiflasher tool, nothing worked.

However, I eventually stumbled on a solution. The Acer devices are made by Eten, and as such, I guessed that the tricks that worked on old Eten Glofiish phones may work on my M900. This trick basically involves editing the Eten equivalent of the CID in HTC phones, which prevents ROMs from other carriers/countries being loaded onto a device.

Ok, so here's how to do it:

1. Go get yourself a hex editor. Something like WinHex will do the job just fine :)

2. Go get yourself a .bin file from the internet, or a .dat file from an official update.

3. Open up the .bin/dat file in your hex editor of choice.

4. Go to the hex offset 0x38.

5. Enter the following hex values: 0A 3D 72 F4
These are the so-called 'magic bytes' that will allow you to load the ROM onto your phone.
 hexedit.jpg (20.72K)
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6. Save the file as temp.bin (note the lower case letters) and transfer it to your memory card and flash in the normal way from the card.

All done :) You should now (hopefully) be able to flash whatever ROM you please to your phone. However, if you use the incorrect ROM, you WILL brick your device.

Enjoy :)