The problem occurs when you have installed both The Observer 5 and The Observer XT on your computer and you score from a video file in MPEG-1 format in The Observer 5. The problem is caused by The Observer XT Decoder Package.
To play back MPEG-1 files in The Observer 5, The Observer XT Decoder Package is not needed. You can disable it (and enable it again when you want to score from MPEG-2 files). Please contact Noldus Technical Support, they can provide you with the files to disable/enable the Decoder Package.