Even if it is created again e.g. by renaming this can cause unexpected error. In this case a restart of the application is needed
Do not delete/move open projects outside of a Nimue Platform based application. This can cause strange error messages. If it happens close all of these projects in your platform app. A restart of the application is not needed.
If you change the main project not all parts of the platform do recognize this correct, e.g. it can happten the processing a session is based on the project which war priviously set as main project. Better restart the application after changing the main project.