The type or namespace name 'Component' could not be found (are you missing a using directive or an assembly reference?), yet references are added

Question

I've just downloaded my favourite extension from Tridion World, which are the generic set of TBBs for a classic implementation: https://sdltridionworld.com/community/2011_extensions/generic-2011-tbbs.aspx.

I've added all the references from the Tridion/bin/client folder, but I'm getting many compilation errors where none of the Tridion classes are recognized:

The type or namespace name 'Component' could not be found (are you missing a using directive or an assembly reference?)
...
The type or namespace name 'ComponentTemplate' could not be found (are you missing a using directive or an assembly reference?)
...
The type or namespace name 'ContentManager' does not exist in the namespace 'Tridion' (are you missing an assembly reference?)
...
etc

I've never had this issue in the past. Why is this happening?

Answer 1

The extension's Solution file (.sln) is set for .NET Framework 3.5, which was fine when Tridion 2011 was current. However, I'm using Tridion 2013, and the new set of TBBs have been compiled against a later .NET Framework version.

Setting the .NET Framework to version 4.5 in the Project properties resolves the issue.