Graph - problem with Visitors (no replies)

Hi,

I have a problem with graphs. Couple of days back all graphs stopped show new visitors (stuck on zero) even there are coming every day. I have several pages and this problem appears on all of them.

Do you have some ideas? (see included screenshots)

Thanks a lot for any information.
Now I have not any idea what is wrong. Basically stats are running correct but graphs are somehow corrupted.

Br.
Marek