I have just created a gallery with WP-SimpleViewer v1.5.4.
I then installed and activated Better WordPress Minify. The gallery displayed OK.
I then deactivated Better WordPress Minify and the gallery still displayed OK.
The problem with your web page is that there is no reference to the required 'swfobject.js' file in the head section.
Try reinstalling WP-SimpleViewer v1.5.4.
Failing that, try deactivating all other plugins you have activated, one-by-one, until your gallery displays OK and you find a conflict.
I have entered sv_core as you suggested, but that does not change any.
This is required for (and works only with) WP-SimpleViewer v2.3.0.
The handle for the 'swfobject.js' script in WP-SimpleViewer v1.5.4 is 'swfobject'.