Is there someone else who also has an empty line between <div class="moduletable"> and <div class="vmgroup">
Didn't had this problem before I update to vm 2.0.2 and joomla 2.5, had joomla 1.7.3 and VM 2.0.0 before.
It's an Byte Order Mark (BOM). You can download File BOM Detector (just Google it) to find wich files containing BOM. Search for Byte Order Mark in this forum, and you will find help.
Yes, I had the same problem, and solved it with the BOM detector... There are BOM's in 2 files you have to fix. Administrator/components/com_virtuemart/tables/categories.php and products.php