It isn't a real bug, but it is very annoying.
It appears on new installation of VirtueMart at Joomla 2.5
The easiest way to fix it is to create folder within Joomla log folder.
1. Create folder in log folder for example /home/path/public_html/logs/safefolder/
2. Copy the above directory path in Global Configuration > System> Path to Log Folder
3. Go to VirtueMart >Configuration > Templates
4. Paste the same path into "Safe Path"