I had this issue a few times already, so I will write down the procedure I follow also as a reminder for myself:
- Replace all of the old solution name with the new one.
- Navigate to Properties under each project and change the Assembly Name and Default Namespace fields to new solution name.
- Go to solution folder and rename all project folders with the new solution name.
- Remove all files under bin and obj folders.
- Solution will not be able to load projects. Remove all projects and add them again.
- Re-build the project.
Source: http://stackoverflow.com/questions/21701297/error-when-renaming-asp-net-mvc-5-applciation