New Events Listings get 404 error

Hi, an event organiser has contacted me to say that his events are being eaten by my site. I took a look into it and while they’re showing on the interactive map, when the thumbnails are clicked on, it goes to a 404 page error.
Also, additional images aren’t showing on the thumbnail pop up window, but broken JPEG link icons are.
I’ve tried to find a similar topic on the boards, but couldn’t see anything.

Any help is greatly appreciated. Btw, I’m not good with technical language, so if you could use layman’s terms with me, that would be ace. Esesentially, speak to me like you would a five year old 😉
Matt