.mp4 files "not supported"

So you're sure it's not memory and you're sure there is no refusal of anything (?) so you're on a good path to figuring out the problem. I won't get in your way. Good luck.

No we're not joking. There are multiple factors that decide program performance. For example, since you refused to give us system specs there may be problems in the GPU, you could have a lack of memory. This is your second time posting and I still have yet to know anything other than you use windows and an mp4 isn't working. I'm unsure of how you're positive that AE is the problem when even you indicate other MP4s are working fine. Unfortunately, after being asked twice you didn't tell us the format of the mp4 so we're hamstrung on helping to that regard as well. And it's not "really stupid" to transcode to a file that is made for production. Your client is giving you files that very very few professionals work with. Making them a more amenable to any post production software only makes sense. Also, how are you sure your file isn't corrupt when, again, even you state other mp4s work fine.

Again, try transcoding. Try it in Premiere or ME (as Kyle mentioned) With your refusal to provide any information other than your positivity that the program is broken - for you and you alone and only on 1 file - it's difficult to give any further advice.  

I am having trouble understanding you guys... do you like asking question just for the sake of it? using pc windows 10 i7-8700k1080ti g1 … how does my specs make you understand the situation better? I need real help from adobe the program is broken I am being fade mp4 files from client it would be really stupid way to go transcoding everything... maybe in a perfect world were I don't have to render the project till the morning... the clip is not corrupt I don't need possible this and possible that... if anybody know what to do please help!!!!!!!!!!!!

Have you tried using these clips in Premiere? In the previous version of AE (which you can definitely still have installed alongside the current one)?

It's possible the problem clip is corrupted in some way, and may have nothing to do with AE. Confirm it works elsewhere to narrow down your variables.

What is the format of the clips?

There's a lot to unpack here and knowing a bit more about your machine would be helpful. Computer specs, OS, etc. Also what's the codec on the MP4? I'd say start by transcoding in AME to a different format - try Cineform of DNxHD or ProRes. I try to never use MP4s in production. It's just not made for that.