Reimporting from Camera for footage already in Timeline in FCPX
The error you are having "Project has missing or offline titles, effects or generators" is kind of self explanatory, the project you are trying to export is missing on of the following from within the project timeline


Title (some text you have put on or used) 
Effect (a fade in or fade out, wipe, etc)
Generator (any one of the build in generators)


so if you watch the project from start to finish you will see the issue, somewhere on the timeline there will be a missing 

If you have not used any of these then there might be something wrong with the project and I would suggest re-doing the whole project again.

I don't think you have any problem with the "media" as such. Normally within FCPX you will see a "red" section where there is a problem.