Thumbnails problem – sencha and nextgen

Hi,

I’ve got some problem with thumbnails, using nextgen.

Thumbnails doesn’t show off e.c.
http://src1.sencha.io/jpg75/250/200/http://marcinek.poznan.pl/upload/gallery/w-drodze-do-maratonu/1.jpg

In Firefox console there’s error:

Failed to load resource: net::ERR_NAME_NOT_RESOLVED

Can I change nextgen settings, to store thumbnails localy, not on sencha site?

Thanks.