Plug-in not working

One of the most read pages on my blog is the list of reasons why a callout won't work. Since the release of CRM 4.0 we do not have callouts anymore, but we're using plug-ins for extending CRM. This article will contain all the reasons that I find on why a plug-in is not working.Error:"Unable to load the plug-in assembly"There are multiple reasons why this error can occur. These reasons include:-