Since switching to the latest builds of Angular 2 (i.e. on github, master), I get warnings as follows about all my components:
NgModule DynamicModule
If you are upgrading a large codebase then none of these answers tell you which component you forgot to add to app.module.ts
The closest answer (if this is your problem) is given by @doubletriplezero
He mentions that compiler.umd.js has some useful info.
In fact this can tell you exactly which component you forgot to import. See
Angular 2 Component is not part of any NgModule
for a fuller answer