views calc

Hello,

I am somewhat new to Rules and am amazed by what it can do. I've got a situation where I believe Rules is the best tool, (I have also considered http://drupal.org/project/computed_field and http://drupal.org/project/views_calc). Any insight you have would be greatly appreciated.

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 $.