How I fixed this issue was manually editing “old_project_name.sln” and “old_project_name.csproj”.
“oldname.sln” and “oldname.csproj” need to be renamed to “newname.sln” and “newprojectname.csproj”.
Open the .csproj file. Change “RootNamespace” to the new name with the spaces removed if you have any, and change “AssemblyName” to the new name with the spaces kept.
Open the .sln and change the “oldname” on line 3 to “newname” (there are two places you need to make this change).
I believe this is case-sensitive, although I haven’t tested it.