If you rename the Folders and/or the *.csproj files. you need to do the following things:

• open your *.sln file with an Text Editor and fix the paths and file names.
• Open all your *.csproj files and fix the the paths of all proejct references
• If you renamed namespace without using refactoring features, you probably will need to fix all the using-Statements in your *.cs files