Problems with importing large backup

I just switched from servers, and now I want to upload my backup via wp-admin – manage – import – wordpress. When I want to upload, it takes a while for the page to load and then it asks me if I really want to import my backup…

It’s a pretty big backup… I just moved another site to other servers and used the importer as well and it worked. I had to run it three times, but it worked (that backup was smaller though).