Just to post I fixed the error message I received from dream up "No CA found by 2nd stage loader, please contact support at dream-multimedia!" on my GENUINE DM800. No thanks at all to the only UK supplier of genuine boxes or dream-multimedia.tv (who im still waiting to contact me, 5days after!), which Im surprised since I expected better support from after taking being so helpful and friendly taking my £356! No thanks to user 'floh' who deleted my original post when asking for help. I Think that user should be deleted! OK rant over!
I found the fix by pure persistence and some support from other websites insisting there was no hardware error, just when I was going to give up!
On a good note, from my experience this is NOT due to a hardware error, it is the Secondstage bootloader becoming corrupt (Prob from an incorrrect shutdown or powercut)I think the main point that other users may have missed is that you need to flash the DM with a relevant image, so dont be afraid to repeat process several times.
NOTE: Before starting confirm your simcard is plugged in correctly, remove top of DM, looking down in bottom right hand corner you should see a simcard with glue on top, confirm that it looks plugged in correctly, you could give it a slight 'poke' if your unsure, but not too hard!
Anyway heres how, I hope I can save other users from the last 5days I've had!!!
- Unplug all connections from DM, only leaving ethernet cable (straight cable if going to a router) and serial connection to your PC, If using a USB --> Serial converter, make sure you have correct drivers installed (Confirm in control panel --> System--> Device manager --> Ports on XP). Note your COM port of your connection.
- Ok firstly use dreamup1.3.3.4, make sure you got 'network' box checked and enter an IP address in the same subnet as your router. this will be the same first 3 digits only altering the last digit (as your subnet mask will be 255.255.255.0), enter a value you know to be free (I chose 100)
- Confirm that you have correct COM port selected
- Select CONNECT
- Plug back in mains on DM (dreamup should load the flashloader and then display the error CA error etc, press OK)
- Dont waste your time on 'Enforcer' or 'dream_fix' (ie. the tools that activate the flash button within dreamup), you will only get the error message that says 'File Too Big' error.
- Press OK on error message (you should now have an IP address assigned to your DM and displayed in the front panel of your DM)
- Open browser window and type in DMs IP in the address bar
- Wait for DM welcome window (I found this took a long time to load, more so after selecting a .nfi image that had a different Second stage BL to my corrupt version, so be patient! 
)
- Note the value of the secondstage bootloader (this is very valid if this is your first attempt at trying the repair and no other firmwares have been loaded)
- Press on 'device upgrade' select a .nfi build that has the same second stage loader that was on your DM before the 'CA error' (If you dont know you'll have to keep rebooting and repeating the process, trying different .nfi images until you match it 
)
- Once the secondstage BL match is made, you'll find that the unit boots past the 'error' message and all appears as it should 
NOTE: This worked for me on my GENUINE DM800 and saved £99+del repair fee. Use at your own risk if your attempting on a clone version (I hear they can be very sensitive with Second stage BootLoaders)