This Windows banner has started appearing at top of all emails containing attachments, both sent & received, and I cannot access any attachment - even the ones I have sent!  All the attachments are wholly innocuous.

I have a Dell IR5 laptop approx. 15 months old, running pre-installed Windows 7, Windows Live, Internet Explorer and MS Word Starter 2010.

All updates are installed up to date. All settings are default- except that recently I was prevented from accessing any docs in my Documents folder

by a MS popup telling me I had to buy another MS product to access my documents. I consulted the MS online forum & learned this was result of a faulty update & could be fixed by changing a setting - which I did.

I see from this forum that the problem with the attachments might be fixed by disabling Windows security - but surely this is not an acceptable fix.

Even the Windows help page says that unchecking the virus protection is not recommended!

What has caused this problem & how can it be fixed without compromising security?