Rollover externally loaded swf does not work

hi,

i have a movieclip that loads another swf.

On that movieclip i want to execute a rollover but that does not work.

My code for the rollover works when i have a bitmap in the movieclip (instead of an swf).

b1.loadMovie("herpa_514903.swf");
b1.onRollOver = function() {
...

what is wrong?