I downloaded ESET NOD32 Antivirus 3.0 (Windows XP) two times and it will not open. I get the following message after download: WINDOWS INSTALLER- This installation package could not be opened. Verify that the package exists and that you can access it, or contact the application vendor to verify that this is a valid windows installer package. No tech support is currently available to address this problem since it is the weekend. Very unhappy I purchased this product. Need some help. Thanks.