Sheet: unable to draw inside when the boundary is darkened by double clicking inside drawing area

My boss has a drawing that he cannot edit inside the darkened boundary of the sheet. When he double clicks inside the boundary to make the boundary darkened, he is not able to edit or add anything.  

If he doesn't darken the boundary, then whatever he draws is not available on the other sheets nor the model.

He is going to send it to me tomorrow, Wednesday morning Pacific Standard Time, to edit and fix. I don't know what is wrong.

I am thinking it has something to do with the boundaries. He has not been setting them and now he is doing so. I think he may have several boundary designations in this drawing and the program doesn't know what to do.  

He has clicked on the "?" help, but it does not give him the information he is looking for.

What do you think is wrong? And how would I fix it?

Thank you!

Cheers!

Patty Shenk