Here are a few tried-and-true ways to prevent this aggravating error message in After Effects.
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One of the most stomach-churning error notifications you can get while working in After Effects is the dreaded “After Effects error: Cached preview needs two or more frames to playback.” Goatman Arts notes that if you’re using a third-party plugin like Element 3D or using 3D cameras in your project, expect the workflow for this solution to be a bit more in-depth. These aren’t guaranteed to work every time, but they may help you prevent the error.
Go to Edit > Purge > All Memory and Disk Cache. Essentially, this is just emptying your RAM cache, and as he so lovingly puts it, cache is just where After Effects stores its results of your current render. So, this is just one possible solution that doesn’t always work, so let’s try out a few other methods to get past this hiccup.
Empty Disk Cache
Above your clips in the timeline, you should see a thin green bar spanning the width (hopefully) of your selected clip. This green bar represents the RAM cache, so by Purging in the previous step, you should no longer see this green bar. Most likely, you’ll see a thin blue bar atop your clips. This is how After Effects writes content to RAM quicker.
To clear this blue bar, go to Preferences > Media and Disk Cache > Empty Disk Cache. This should clear all renders. He also recommends hitting Clean Database and Cache while you’re still in the Preference window.
A simple yet sometimes-overlooked solution to this problem lies with how many applications and programs you have running while working in After Effects. Also, try changing the quality of your preview footage from Full to Half or Third. This might help with rendering.
Re-Importing Rendered Clips
This one is a bit of a stretch, but you could try rendering out what you can and re-importing the clip into the timeline. This is a perfectly viable solution to the problem, but it is a major disruption to your workflow. Select Lossless in your rendering queue, then change your Channel in Video Output from RGB to RGB +Alpha. This will give the clip a transparent background so you can re-import it back onto your footage.
One last tip: Goatman also recommends going to Preferences > Memory then uncheck the box next to “Reduce Cache size when system….”