What type of video are you using on your timeline? What kind of camcorder did it come from?
Also, how much RAM do you have and how much free, freshly defragmented space is on your hard drive?
This is aimed at Premiere Pro, but may help
A link with many ideas about computer setup http://forums.adobe.com/thread/436215?tstart=0
Many of the ideas at the next link are generic enough they have helped some Non-Premiere users fix problems
Work through all of the steps (ideas) listed at http://ppro.wikia.com/wiki/Troubleshooting
If your problem isn't fixed after you follow all of the steps, report back with the DETAILS asked for in the questions at the end of the troubleshooting link
Welcome to the forum.
If the error was along the lines of "Failure to Return Frame," that is often because there is a gap in the Video. All Clips should be butted up to each other. Go to Timeline View Mode, and then hit Home (to get to the beginning). Zoom in on the Timeline. I'd probably toggle Thumbnails to either OFF, or to only show First & Last Frame. Hit the PageUp key to step through the Timeline, one Clip at a time. If you have zoomed to the Frame view level, you should see the gap. You want to close this up. If you cannot see the gap (they can be tiny), the using the PageUP & PageDn keys, step through again, and watch the CTI (Current Time Indicator) to see if it "hiccups," or seems to "jutter" between Clips. If it does, you have found your gap. Look for any more.