If you have Intel, there's an update available for Intel Application
Accelerator; this hopefully might help, depending on system requirements.
Consider updating your current Application Accelerator Driver, to rule out
this possibility. Make sure system requirements are met, and that an update
is actually necessary. This option might be available through the computer
manufacturer, pending warranties, etc.
About the viral scan, it's good to check. Consider scanning for spyware and
parasites, as well. Viral Scans do not pick up on them. Check your Firewall
settings, and make sure nothing is altered.
There was also mention of NAV being turned off for the sake of
functionality. This could be another part of the problem. You should be
able to proceed with applications, without having to leave the system
vulnerable. Check their site for troubleshooting, so that you might keep it
running. Maybe it's time to consider changing brands. Not faulting the
product, but if it's incompatable, another might be better. This is optional.
Make sure you have valid and signed Active X files only.
Anit-spyware or parasite prevention and removal, might require purchasing
third party software. If possible, it would be more feasible, to purchase
through your current Anti-viral and Firewall provider. Software
compatability is a serious and necessary consideration, to avoid creating new
problems.
There's one parasite out there (can't mention the name), that downloads into
your Registry and starts overwritting files every where, until it slows the
system down. There are so many, that it is impossible to manually remove
them.
Still others might have different options to offer, but it's a start. This
is not one to overlook, because it might spread to other areas.