Today i noticed Running .Net applications on Linux with Mono and the author wrote the following:
I found that on Debian at this stage I got an error: The assembly mscorlib.dll was not found or could not be loaded. It should have been installed in the ‘/usr/lib/mono/2.0/mscorlib.dll’ directory. I cured that by executing:
$ cd /usr/lib/mono
$ sudo ln -s 1.0 2.0
There is only one error, and it’s in the PEBKAC category. I can understand that the author couldn’t find the TargetFrameworkVersion tag in his project file and generated 2.0 code. What i don’t understand is that he didn’t notice the Other Downloads section and that there are Debian packages available with support for the 2.0 runtime. Ok, apt-get might complain about the packages and you would have to add a key to your keyring as following before you can install the packages:
gpg –recv-keys 7127E5ABEEF946C8
gpg –armor –export 7127E5ABEEF946C8 | apt-key add -
How hard is that? 
Today i had to run this same procedure again:
# notice that the keyserver, recv-keys and export are starting with two dashes ( – )
gpg –keyserver hkp://subkeys.pgp.net –recv-keys 7127E5ABEEF946C8
gpg -armor –export 7127E5ABEEF946C8 | apt-key add -