In the comment on that video it says..
if you get the error "can't find panelizar.scr" run Eagle as administrator.
It looks like the ulp creates the .scr on the fly as it operates, but I suspect Eagle will throw up an error if you exceed the fews board size limits.
Just for the record, there is now a workaround to Eagle board size limits.
github.com/p12tic/eagle-brd-merge
It produces an eagle board file containing several sub-boards. The resulting board can be larger than 100x80mm limit and fully editable as long as no component is moved, so for example it's possible to partially connect the sub-boards to satisfy a common requirement of low-cost PCB houses.