Mask affecting preloader?

I am wondering if a mask on an external swf (the mask is masking two MCs) is affecting the ability of a preloader.

I have a main movie

i load an external swf (video) into an empty MC and it preloads fine

in video i have a slider navigation system. that slider navigation system has empty MCs in it.

I press the button in the slider navigation system and it loads a an external MC into the empty movie clip.

However the preloader doesn’t work for this second set of loading.

for the code I have

_parent.container.general.gazebo (the container is the eMC on the main movie, the general is the MC on the video swf and the gazebo is the eMC in the slider)
the slider is covered by a mask however, and I was wondering if that is affecting the preloader of the second eMC.