Websites not loading, 138 error

Hi
I have yesterday installed Windows 8 Pro over my Windows 7Pro, and all appears well, apart from web browsing. My computer loads some websites fine, but most give the error 'Error 138 (net::ERR_NETWORK_ACCESS_DENIED): Unable to access the network.'. The behaviour is the same with Chrome 23 and Internet Explorer 10. I have Bullguard 13.0.255 installed, and Windows firewall is disabled, but I see no difference if I disable Bullguard's firewall.

Any ideas?
Andrew
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Tech Support Guy System Info Utility version 1.0.0.2
OS Version: Microsoft Windows 8 Pro, 64 bit
Processor: Intel(R) Core(TM) i5 CPU 760 @ 2.80GHz, Intel64 Family 6 Model 30 Stepping 5
Processor Count: 4
RAM: 8190 Mb
Graphics Card: ATI Radeon HD 5700 Series, 1024 Mb
Hard Drives: B: Total - 1430796 MB, Free - 110475 MB; C: Total - 953766 MB, Free - 273464 MB; F: Total - 2861575 MB, Free - 881253 MB; I: Total - 305163 MB, Free - 164926 MB; Z: Total - 1430796 MB, Free - 826305 MB;
Motherboard: ASUSTeK Computer INC., P7P55D PRO
Antivirus: Windows Defender, Disabled // Incorrect, I have Bullguard 13.0.25