Dapper 6.06.1 to Hardy 8.04.1 upgrade problems

[Andy Cleeves]

Hi All,
( Note to admin. I first posted this before I had registered as a user. 
I have deleted it and re-submitted it here).

I'm having problems upgrading from 6.01.1 to 8.04.1.
I'm doing a parallel install before updating a working server on which I 
want to run mono/asp.net with mysql/connector.
I installed 6.06.1 and installed php5, apache2 with mono-mod, mono, 
xsp2, and mono-dev on a parallel system for  test purposes.
I have done a full update first and then installed update-manager-core.
Then I ran do-release-upgrade from the command line.
The upgrade runs and then it falls over where it calculates changes.
When I look in the /var/log/dist-upgrade/main.log I see:

2008-12-30 21:50:37,198 DEBUG The package 'ubuntu-desktop' is marked for 
removal but it's in the removal blacklist
2008-12-30 21:50:37,212 ERROR Dist-upgrade failed: 'An essential package 
would have to be removed'


I'm using the following repositories:

deb-src http://gb.archive.ubuntu.com/ubuntu/ dapper main restricted
deb http://gb.archive.ubuntu.com/ubuntu/ dapper-updates main restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ dapper-updates main restricted
deb http://archive.ubuntu.com/ubuntu/ dapper universe main restricted 
multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ dapper universe
deb http://gb.archive.ubuntu.com/ubuntu/ dapper-backports main 
restricted universe multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ dapper-backports main 
restricted universe multiverse
deb http://security.ubuntu.com/ubuntu dapper-security main restricted
deb-src http://security.ubuntu.com/ubuntu dapper-security main restricted
deb http://security.ubuntu.com/ubuntu dapper-security universe
deb-src http://security.ubuntu.com/ubuntu dapper-security universe



During the upgrade I get the following:

.
.
.
Updating repository information
WARNING: Failed to read mirror file
Done http://gb.archive.ubuntu.com hardy Release.gpg
Done http://gb.archive.ubuntu.com hardy-updates Release.gpg
Done http://gb.archive.ubuntu.com hardy-backports Release.gpg
.
.
.



Thanks in advance.

Andy