Mono broken after installing Nant

I installed Nant because it's required by OpenSim. However something seems to have gone wrong. Now I can't remove it, and my Tomboy notes refuses to launch.

This is the problem with liblog4net1.2-cil:

The following packages will be REMOVED:
  liblog4net1.2-cil
0 upgraded, 0 newly installed, 1 to remove and 1 not upgraded.
1 not fully installed or removed.
After this operation, 360kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 241903 files and directories currently installed.)
Removing liblog4net1.2-cil ...
E: File does not exist: /usr/share/cli-common/packages.d/policy.1.2.log4net.installcligac
dpkg: error processing liblog4net1.2-cil (--remove):
 subprocess installed post-removal script returned error exit status 1
Errors were encountered while processing:
 liblog4net1.2-cil
E: Sub-process /usr/bin/dpkg returned an error code (1)

Which effects Tomboy:

afrodeity@afrodeity-desktop:~$ tomboy

** (/usr/lib/tomboy/Tomboy.exe:28595): WARNING **: Missing method .ctor in assembly /usr/lib/tomboy/Tomboy.exe, type System.Runtime.CompilerServices.CompilerGeneratedAttribute

** (/usr/lib/tomboy/Tomboy.exe:28595): WARNING **: The class System.Runtime.CompilerServices.CompilerGeneratedAttribute could not be loaded, used in Tomboy

** (/usr/lib/tomboy/Tomboy.exe:28595): WARNING **: Can't find custom attr constructor image: /usr/lib/tomboy/Tomboy.exe mtoken: 0x0a0005b6

** (/usr/lib/tomboy/Tomboy.exe:28595): WARNING **: The class System.Collections.Generic.Dictionary`2 could not be loaded, used in mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089

Unhandled Exception: System.TypeLoadException: A type load exception has occurred.

How do I fix this? Is the cache corrupted as in a failed install, or is Mono broken?