SOLVED! I had this exact same issue today. AE CS5, Win 7 Home Premium 64 bit, Alienware M17x / 2.5 Core2 / 8GB / 1GB Nvidia card.
My RAM and audio previews were suddenly limited to 1 frame. I tried rebooting, clearing my preferences, and nothing worked until this article saved my neck…
All I had to do was boot into safe mode (hold F8 while booting), open and close After Effects, then boot normally. Problem solved, and I can do a RAM preview longer than 1 frame.
https://forums.adobe.com/message/2859431
https://acbstudios.com
Web • 3D • Motion
Alienware M17x R1