Without exact system info and render settings as well as more info about your files nobody can say anything.
Can you use the Save RAM Preview option?
Thanks for the help guys. I've dug in a little deeper and I think I have two issues:
1) I'm rendering out multi-layer EXRs, and I've found AE generally quirky dealing with EXRs
2) I tried a test loading a JPG sequence on 10s and I don't get the errors I get with EXRs, but still AE does not handle partial frame ranges elegantly. If I use RAM preview, AE will substitute color bars for the missing frames for example, instead of holding frame 1 for a few frames, then frame 11 for a few frames, and so on...
I'll continue reading forums and docs to see what is the best way to deal with partial frame ranges... Thanks all!