Browsers are comntinually blocked by Norton 360.

Both chrome and IExplorer are not working properly. Norton keeps blocking the websites I visit regularly saying they are not safe to visit.  Facebook for example or Youtube. funnily enough they work every now and again then a block is set after I have been on the site for a few minutes. In Iexplorer I can look at details of block and it displays the Site as OK but still won't let me access it. 

I have reinstalled Chrome and Norton 360. but this has not helped in the least.

HELP