I've spent the last two days reading here and on the Internet about this issue. Nothing is helping resolve the problem.
This issue just started recently--several days ago. It would come and go, depending on the project. Now, it's here to stay. I cannot export a sequence! If I remove all the stills (PNGs) and remove all the title graphic clips (NewBlue Titler 2.0), leaving nothing but the raw camera video, THEN it will export to H.264. This is unacceptable, to say the least.
Does anyone (i.e., Adobe) have any suggestions as to why this is happening--anything "new" that is?