Zoom effect skewers pics

[Pizaster]

Hi All -

 

I am having a very serious problem. I am using the zoom effect on almost all pics in my slideshow (to create a Ken Burns effect) and the problem I am having is that once I click on the zoom tag, the photo automatically becomes a thumbnail or the screen just goes black. If I play with the effect I may get it to work, but on some pics it simply won't work. Does anyone have any ideas. This is so completely frustrating. I am using simple jpgs, do I have to change the photo format??