It may occur, that you update an EA Addin, and instantly it fails to work.

In my case, it failed while writing to the settings-file located in user-temp folder.
Although it was build for .NET Framework 3.5, the error message was something like this:
“Could not load file or assembly ‘System, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089’ or one of its dependencies. The System cannot find the file specified.”

After researching the internet, I ended up with the following solution:
delete the content of the folder “C:\Users\<username>\AppData\Local\Sparx_Systems_Pty_Ltd”

this is, where .NET stores information about your EA-addin. It will be recreated having the correct values on next EA start.

And here is the excerpt, which lead to the exception:
<section name=”LL.EA.Plugin.dll” type=”System.Configuration.ClientSettingsSection, System, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089″ allowExeDefinition=”MachineToLocalUser” requirePermission=”false” />