That's a Quicktime error. since you have not provided any exact info otherwise, we can't tell you anything more than that. You know, stuff like storage locations, exact footage used, comp and render settings and whatnot.
Thanks for the clue. I'll reinstall Quicktime and see if that helps. Reason I didn't specify any of the stuff you mentioned is because it doesn't matter, as I stated in original post. I can change settings all I like, change source, destination, cache location, all on separate drives, etc. ad nauseum .. makes no difference. Works just fine sometimes, others not. Works well if I create a new logon entity but then I have piles and piles of system wide authorizations to go through, and the fact that it is a NEW problem that started happening after no notable system changes, has me befuddled. Worked fine/reliably before, and I didn't change anything. If it keeps happening I get to go through complete system re-install, which is horrible. AE is the only program having these problems.
Update: Since reinstalling Quicktime I have not seen the error (after restarting the machine).
I hope this post does not jinx it, but so far so good.
If it pops back up, so will I.
Until then, thanks, and be well!