You should try calling the slider.js from the helloslide block.
Go to CMS->Static Blocks and edit the helloslide code, in the first line make the call for the slider.js.
Please for any doubt check the one you used before, we have already solved this once try to find the previous solution.
Manrico, please look your site!
The error appear because another extension or configuration wrote other jquery after than slider.js.
I wrote this in CMS – Statics Blocks – HelloSlide (before the images) and fixed: