Parser Error Message: Could not load type ‘sometype’

I am experiencing an error that I am unable to resolve for some time now. I was wondering if someone can help identify the cause of this error? I am completely new to asp / asax. After some research, I think that the error I am getting is due to the web application trying to use outdated code. I was thinking to rebuild the c# file using Visual Studio and/or the entire project. However, I am completely new to C# and asp, and was wondering can give me some suggestions if this may fix the problem and/or if there is an possible alternate solution.

WebAPI controller inheritance and attribute routing

I have few controllers that inherit from the same base class. Among the different actions that they don’t share with each other, they do have a few that are completely identical. I would like to have these on my base class because they all work completely the same it’s just that they’re accessed through different routes.