Disappearing Norton toolbar...

My Norton Toolbar keeps on dissappearing.

 

When I open the browser it's there, but every so often, when I go to a new webpage, it dissapears.

 

Not noticed any definite pattern, but seem to happen mostly when I open 'Open in new tab' - and have had it where on some tabs the Norton toolbar will be there, but switch tab and it goes, switch back and it's back...

 

Anyone know what's going on?

 

Browser: Internet Explorer (version 8.0.7600.16385)

OS: Windows 7 Home Premium OA

NIS: Netbook Edition 2010 (version 17.5.0.127)