Codec errors after exporting in Premiere PRO

I tryed to export a video of more than 1 hour, and multiple times when it was done, the file type was not mp4 like it was set in the export settings. After multiple tryes it finnaly exported the mp4 file, but after the 15 min mark it said that "it uses unsupported codec settings", what can i do to export the whole video in mp4 format without this problem to occur again? The original clip format is "AVC_1920_1080_HP@L42",  which is like H.264, the format that i exported it.