I have recently experienced problems involving BT Netprotect Plus. The restart following a "latest version" update now always results in windows 7 crashing. A blue screen informs me that a problem has been detected and windows has been shut down to protect the computer. I can only restart the computer via safestart and then a system restore to a recent date will recover the computer until the next software upgrade/restart. BT advise that the problem is not with BT Netprotect plus or the Broadband connection. They suggest it is caused by a problem with the PC's operating system. I expect that BT's advise is correct, but would be interested to hear from anyone else who has experienced this problem or can offer any advise.
Have you tried another AV? Although NetProtect works fine for some people, many have had insoluble problems with it. In truth, it's no better than many of the free AVs available and suffers from being a huge resource hog, especially on less powerful computers. Microsoft Security Essentials is recommended by many on this forum, supplemented by an occasional scan with Malwarebytes Anti-Malware.