The message is telling you that there is corruption at or around frame 50401. For a 30 fps project, frame 50401 would appear at or around the 28 minute mark.
Sometimes the corruption can hide in a transition, or a title, or maybe an incompatible format. Titles from third party vendors can sometimes cause issues.
Expand out your timeline to full out, and scroll through slowly again around the 28 minute mark (assuming the usual 30 fps project), looking for artifacts, black frames, white flashes.
Also, you can try making a duplicate of your project, deleting the second half of the timeline, and then exporting. If you get a bad export, cut in half again and export until you get a good export. The part that you cut away would contain the corruption. If you get a good export the first time, cut the other half in half and export, and see if you can narrow it down per the above.
If you have other than a 30fps project, use this procedure to find the point in minutes at which frame 50401 appears:
Frames (i.e. 50401) divided by Frame Rate = seconds at which 50401 appears. Divide the seconds by 60 to get the point in minutes at which fram 50401 appears.
-- Rich