There's not enough information about your project to make a better guess than disk cache problems or uncompressed video rendered and played back through your media player.
I have no idea what you mean by 'they jumped away.' Keyframe data does not change when you re-open the project. We need to know specifics and see a screenshot.
So I'm using
This would be an example for the "jumping keyframes".
Yesterday, when I turned my Computer off, it was alright (I had to do it again, since jumped away yesterday)
But today again they are completly wrong.It's as if the Keyframes switch places with each other or something. I tried puling them to an earlier/later frame, but it's not like they are delayed then.
And yesterday, when I tried to render it I only changed the settings to QuickTime and RGB+Alpha. Didn't do anything else.
I didn't really touch the settings for the program either.
The only thing, I did change was that the keyframes stay constantly in the project (so if I delete one at one point they still stay in the rest of the comp)
Sorry, but since I've got a german version I'm not sure how helpful screenshots would be...And of what exactly I should make them
Screenshot of your AE project with keyframes revealed. Press the u key twice (do not know the german equivalent but it may be the same) to reveal all changed properties for each layer and send us something like this.
Then close AE, re-open your project and send us a screenshot of the same comp with changed keyframe values. If you can park the CTI on a keyframe that changes values so we can see what is going on.
It would also help to know what you are animating. From the screenshot I think it might be the mask paths but I don't know.
Your mask keyframes are not changing. Your footage is. What is the source of the footage? What codec?
Try rendering the original footage to a production codec or an image sequence and then replacing it in your project.
Look at this animated gif carefully and observe the masked area. It never changes. It would even look better if you had selected the layer in the second screenshot so we could have seen the mask path. (click on the gif if it is not animating.)
The length in and of itself shouldn't be a problem. It's possible that the codec is being screwy within AE for some reason. CS5 usually handles h.264 video alright (much better than CS4), but who knows?
Is your CS5 updated to the latest version? If I recall correctly, there were some bug fix updates released for it that helped when you were working with codecs that weren't production codecs. You should be on version 10.0.2. If not, go forth and update!