Showing errors in a ECL mountpoint

External Content Library (ECL) Providers can raise error messages in a very user friendly way. The mountpoint can show a list item with the error message when it occurs and error and cannot get data from the external system. This avoids confusing the Tridion CME user with an error message in a popup and having an empty list.

This idea came up in a Tridion.Stackexhange Q&A on http://tridion.stackexchange.com/questions/3097/raising-an-error-from-a-ecl-provider

The solution is implemented in the Flickr ECL provider. See this commit to discover
how this works in more detail.

Basically the Flickr mountpoint will return a error message in a IContentLibraryListItem which represents the error. This ErrorListItem object will have it's own DisplayTypeId so that it can show error icons.