I have had problems installing BD 2008 and BD 2009. I use the following procedure to get problem free installation and problem free use.
Download the Bit Defender uninstall tool
Do the uninstall from the tool
Reboot as indicated by the tool
Run the uninstall tool again to pick up any remnants (might have been in use the first time).
Reboot again only if the tool indicates it.
Next, install the product.

You can get the Uninstall Tool from this page:
http://kb.bitdefender.com/KB333-en--How-to...itDefender.html

as an added note if your operating systems user account name has any symbols in it @#!$%^ ect. many programs wont recognize the path , so set up a new account.