Can't export video from After Effects

I've made a video in After Effects, that is ca. 40 minutes long, and the export via Adobe Media Encoder won't work for some reason.

The export takes about 20 hours with Adobe Media Encoder (my computer is a bit dated), and I do get a file, that is 4.29 GB big, but I can't play it back, neither on QuickTime Player nor on VLC.

Here are the Codec details:

• H.264 (in MP4)
• 1920 x 1080p, 25 FPS, Progressive, PAL
• "Render at Maximum Depth" enabled
• Profile: High, Level: 4.2
• 20 MBit/s, VBR

The restrictions:

• Video file must be less than 7 GB
• At least 20 MBit/s bitrate
• H.264 preferred

The export works perfectly fine when I only render 10 minutes of the video; therefore I thought the 20 hours of rendering might be too long, so I reduced it down to 2 hours (using some tricks), which again doesn't work (4 GB file, can't play).

I'm not too experienced with videos, so I really can't figure out, what the problem is. Thanks in advance for any help.