Cannot start new batch download

[Cannibal]

I've downloaded a batch 5 minutes ago but for some mysterious reason I cannot start a new one. Each time I enter the url using the batch descriptors (I've checked I'm using the correct ones several times of course) the download popup expands for a second and indicates there is something wrong with the url box by indicating it with a red line. The strange thing is that I've tested both the start url and end url for the batch and both work and are active.

Any thoughts?