views calc

I´ve recently installed views calc (I´ve got last stable release of views and cck), and got a nasty error:
warning: Invalid argument supplied for foreach() in .../sites/all/modules/views_calc/theme.inc on line 160..(*)
But, sometimes, randomly, the error won´t appear, but the view won´t work either.

I´ve look for that error at the forums, and found nothing.
I´m attaching the strange and totally random behaviour of Views Calc as a png. It should show the sum of the one column with the prefix $.