There is no way we can even guess what went wrong without some information about your comp, your render settings, and any error messages or the render log file because there are hundreds, maybe thousands of things that can cause a render to fail from memory and cache problems to bugs to operator error.
There's no error on the log file, as far as the program concerns it rendered everything correctly.
My machine is an imac (iMac12,2) with 32gb ram and AMD Radeon HD 6970M with 2048 mb of VRAM.
My current settings (for approvals) are QT with H264 compression with audio output set to Auto and I'm rendering at half res, which in this project is 1024x1024 px, the render is taking approximately 4 and a half hours with MP off, last friday I tried it on and after 7 ours it only had less than 25% done and it said it still had 27 hours to go, so I canceled it and switch to MP off instead, it finished the render (incomplete, I found out today) in 2 hours and 38 minutes, plus 42 minutes for the missing portion this morning, which came with no audio.
I haven't rendered uncompressed or prores yet, but I will be doing tonight to see if that yields a different result.
Is this enough or you need more specifi data like solo switches settings, guide layers, etc?
Something here doesn't add up -- you can no longer render to H.264 within CC 2014. That capability is gone. I'd be interested to know how you're doing that.
I'm not rendering using 2014, but CC, I think that 2014 is messing somehow with the background processes from CC, but it's only a guess, I have no basis to affirm that.
Also, I'm not rendering to h264 but rather a QT with h264 encoding, at the end my extension is .mov, not mp4.
The Quciktime container for h.264 compression is buggy. I would never use it, especially from the render cue. If you must render with the render cue pick a production codec and then compress using the AME.