Hi,
Never seen this problem before, but i found this forum topic:
forum.virtuemart.net/index.php?topic=104707.0
This is what they say about it:
As i see the $category->products_per_row does not return the products per row, but zero, for that reason that error appears.
make sure you didn't enter 0 for the "product per row" field through the
Virtuemart Configuration >> Templates tab. Make sure your "configurations" are saved properly.
About the second issue,
There are 2 ways to solve it;
1 - Upload picture for manufacturers, make sure all manufacturer have pictures.
--- OR ----
2- Open the "Flexible VM3 Template" plugin, and
disable "Show Manufacturer Logo"
FYI: check all parameters in the plugin backend and when you see "Show Manufacturer Logo", disable it --- both for category and product details page
Regards.