We can't know. You are losing yourself in vagueries instead of providing solid information. I don't know what a "high-spec" PC is supposed to mean. In the 1980s, an Amiga 500 was high-spec, too. And then all the other stuff - version of AE, footage used, comp settings, render settings, MP preferences and what have you. You need to do a much better job at providing all those details, possibly along with a screenshot of your timeline to illustrate the issue.
If you mean that the ram preview stops at about 1:15 then that's probably normal. If you mean that you can't see anything past 1:15 when you move the CTI beyond that point then you have a problem that is probably related to the out point of the layer you have time remapped. If you try a test render and the video stops at 1:15 then you have a problem in your comp.
We have to see your timeline with all of the changed properties of your problematic layer revealed. Select the layer giving you problems, press the U key twice and post a screenshot. Maybe then we can figure it out.
Ok well as I said I have not been using the software for long so I do not know if this was an easy fix or not, so I wasn't sure if all that information would be relevant, so forgive me. Here is the information you might need:
CPU: Intel Core i7 4790K
Motherboard: Gigabyte Z97X
Graphics: NVIDIA GeForce GTX 770
OS: Windows 7
Version of AE: CS6 (18.104.22.1688)
These may be the layers causing me issues:
I have updated my other post, giving a link to the layer that may be causing problems.
You do not have a high spec machine. 8 GB of RAM is the minimum I would suggest for running AE (and the Adobe AE system requirements page says the same thing).
And your description sounds like it is a RAM issue.
Add more RAM.
If that's not possible right this second, you do need to change your multiprocessing settings. You are not leaving any CPU cores for any other processes. This can cause problems. Go through this: FAQ: What are optimum memory settings for best performance in After Effects?
If that doesn't help, with so little RAM, you also might consider turning off multiprocessing entirely.
If that also doesn't work, try going into the "secret" preferences and set it to purge after so many frames.
What are your output settings? Also, we don't even know what version of AE you're running (well, we know it's not the latest one, but that's all we know). Version number down to the last decimal would be helpful. For example: at home I'm running 22.214.171.124 and at work I'm running 11.0.4 - what are you running?
a) Convert the time-remap to keyframes using the respective animation assistant.
b) Convert your WMV file to a more suitable format like an image sequence to avoid decode errors.
c) Pre-compose the image sequence to a longer duration/ loop it.
These are some pretty obvious shortcomings in your current setup. The rest is subjective, but I would have to agree with Szalam - 8GB is certainly not high-spec for AE or any compositing work for that matter...
Thanks for the help. I gave this number: '126.96.36.1998' earlier which I found by navigating to help, and then 'about after effects'. Is this not the version number?
Thanks for your help, much appreciated