mhh… seems to depend on the machine the swf is running on …
I found the solution (mhhh. ok a hint what caueses the prob… not really a solution) at the macromedia site :
"SWFs with high frame rates may slow system performance
Product: Flash
Platform: All
Versions: 5.0 and above
ID: 14981
Issue
Movies that have been assigned a high frame rate (30-120 frames per second) may cause system performance to slow. This occurs when the Macromedia Flash Player 5 (or above) is used to display the movie.
Reason
Flash Player 5 attempts to achieve higher frame rates than previous players. As a result, the system may be forced to work too hard to achieve this higher frame rate. This can reduce overall system performance.
Solution
To prevent this, set the frame rate of the movie close to the actual target rate. Use 15 to 18 FPS (Frames Per Second) as a guideline"
… ups i really need 100 frames to generate some “special effects” … but nw … mhhh…