I am having similar issues as well. Here is my system information. I am using the REDCINE-X_build_54_win version on Windows XP, service pack 3, E8400 GHz processor, 3GB of Ram showing (4 GB are installed). My video card is NVidia GeForce 9600 GT with 1GB of memory on board.
When I open Redcine X everything is fine until I scroll over any r3d file. After the mouse hovers over any r3d file the footage plays for maybe 2 seconds max, then the footage either freezes or goes black. I can still load the file to the time line and export but it is also black as well. Has any one else experienced this? If so have you found what the solution is?