9.10 Hangs on upgrade(mono gacutil)

[rhinovirus]

While upgrading to 9.10 my instillation hung, consuming ~70% of the CPU. The offending process appears to be gacutil.exe, which has been complained about previously for hanging.

Here is a relevant snip from ps aux:
http://pastebin.com/f40fb8ab7

I saw it requested in another thread, so here's the contents of /var/lib/dpkg/info/mono-gac*
http://pastebin.com/f55090610

I killed it (bad, I know, but it was running for many hours), and the following message popped up in the upgrade screen:

W: The assembly mscorlib.dll was not found or could not be loaded.Any ideas?

[directhex]

Try installing libmono-corlib1.0-cil (apt:libmono-corlib1.0-cil)

[rhinovirus]

Try installing libmono-corlib1.0-cil (apt:libmono-corlib1.0-cil)

And what would you say is the best method of installing another software package during an upgrade? The apt repository is locked, no?

EDIT:
After the upgrade - during which I just killed mono every time it hung - I purged all mono packages and slowly started to reinstall them. I started by only installing corlib and it's dependencies (including gac). This eventually started to hang again on libgconf2.0-cli and all libraries after that during the 'install assemblies' stage.