Check frame rates, check codecs, clear cache. You have not given us any information about your project. There are lots of things that could be causing your problems, most of them workflow related.
It looks like you are trying to replace a composition with some footage. That's is not the way to do it. The missing footage resides in the composition. Open the comp with the missing footage and find it there, then replace it.
Yeah Rick that was a brain overload on the replace screenshot. When i went into the folder it did correctly. However it was the 4th time i had done it.
built a comp in PS cs5 then imported that into AE then animated (1080p30)
I animated several comps before even opening PPro.
Then i opened premier (AVC 1080p30) and sequenced the comps to match the V/O.
There was a lot of going back and forth with AE due to it being timed to voice.
I rendered in AE (No Mercury Playback)
Then exported h264 1080p29.97 and i also did Mpeg2 1080p29.97
On export it will loose the file. However when i replace the file in AE it will export smoothly until I close both AE and PPro.
When i open the next day and try the export it jumps back to there being a missing file in AE cs5.
On todays replacement i actually moved the file to another folder on another drive to see if it would do the same when i reopen later today.