I have a created a windows game library to include the basic stuff of XNA so I don't have to write them again(like cameras). Every thing was working fine until I added a Map namespace with a MapReader class. every since then every class and namespace I add to the library flashes the error : Error 1 The type or namespace name 'namespace' does not exist in the namespace 'GameLibrary'. I do not understand the problem. Although there is a TextInput namespace that works fine.