'Almost' sounds like your DVD drive isn't reading the data off your discs, hence it can't complete, because it can't copy the data over. (tho I don't think this is the case)
...Although saying that, I've had the same errors as you mention, but only when I try forcing things that I shouldn't with a Debug Kit fitted with a 120gb HDD.
...In the end the 'only' (easiest) way I could get round the problem was to install the oldest recovery disc I had, which recovers automatically.
...This worked mainly because the early recoveries have less data to copy over and they 'force' the (correct)flash kernal/dash without giving you a choice. (where as later recoveries you can choose options in the recovery process which can bugger the process up, with incompatible choices/a fussy Xbox)
My advice would be use the oldest recovery you can find (Aug 2001 (final) - May 2002 are ideal ones), THEN recover using a a later one, this gets round the errors you mention with ease.
Hope this helps.