Do you use compressed sources? These issues are familiar with some AVCHD variations in CS4. Though pretty much all of them should have been fixed in CS5, you never know... Definitely check whether the latest 10.0.1 update has been applied. Otehr than that this may simply be a CoDec issue when rendering the file. What settings do you use exactly?
I have the problem with all AVI / with quicktime export (no conpression)
With a export with h.264 codec, the problem disapear...
About my sources, it can happend in any case, because as I told you, with just an emplty composition, I have the problem.
I will try to download the last update.
Ah, sorry. I overlooked that particular sentence. Do you have any CoDec packs or alternative media players installed on the system? They might interfere. Otehr than that I could only think of issues with hardware acceleration, so look into turning off these options in Quicktime and MediaPlayer. also perhaps try to save your files to a different location and, if you use it, turn off MP rendering.