This may be old news to some of you but it wasn't to me.  If you're planning to run the Windows 10 upgrade install (and maybe you are, before the free offer expires in a couple of weeks), first do this: go to the C:\Users\[userName]\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Orbx folder, and delete the file called "TODO."  If it's present, it's likely to cause an installation error (the prompt is "Installation failed in the First_boot phase with an error during migrate_data operation", with error code 8007004-300D).  The file isn't functional, and per ORBX, can be deleted with no ill effects.  The fix is described in detail in this thread over on the W10 OS subforum.  But I had no idea about it, and only found it when, after a lot of hair pulling, I googled the error code and got pointed back to Avsim.  Posted here since, if you're an ORBX user, you can take the precautionary step of deleting the file and save yourself some trouble. Hope this is helpful.  

Very helpful. I also learned it the hard way when I upgraded. 

Which version of Windows are updating from?  I don't seem to have that file in 7. 

Updating from Windows 7. But not every installation has it. I'm not sure under what circumstances it's created. It's common but not universal. If it's not there, then chances are you're safe to proceed.