Strange Wifi problems on VPCZ11X9E

[heackro]

I have a VPCZ11X9E, had it for 2 yrs plus, wifi has always worked fine in various (safe) places I visit regularly. 

Suddenly in some of these locations, the wifi no longer works.  It appears to connect ok, I get the 5 bar signal strength and it is showing as connected in the network & sharing centre, but there is a yellow exclamation mark on top of the 5-bar symbol, and the connection does not work.

If I hard wire it with an ethernet cable, it connects fine.

I visit about 6 wifi locations regularly (e.g. home, work, train) and it now works fine on about half of them, but on the rest I get this problem.  Nothing has changed with any in terms of passwords etc.  

E.g. it is working at work but no longer at home.  I swapped the routers and the problem remains so i know it is not them at fault.  I called my home ISP (BT) and they accessed my PC remotely but couldnt find anything wrong with the network, saying it was a hardware problem.   They checked all the settings via the nw & sharing centre and all was in order.  All other devices at home connect to the wifi without an issue, so i know for definite its my laptop.

I have downloaded the latest Wifi driver from Sony but it made no difference.

Any ideas please?  All suggestions would be gratefully received.

[heackro]

I emailed Sony helpdesk and they sent this fix, which so far, has worked.  Thought I'd post it, in case it helped others with same problem:

Please uninstall the Microsoft Virtual WiFi Miniport Adapter, (Start/right click Computer/Properties/Device Manager/Network Adapters) it will then reinstall itself when you reboot. In addition, please apply the steps below:

1.           Go to control panel and open Network and sharing center.

2.           Click on Change adapter settings.

3.           Right click on the wireless adapter and click Properties.

4.           Click on TCP/IP version 4, and then click on properties.

5.           Ensure that all the TCP/IP & DNS settings are obtained automatically. If not ensure that the correct settings are logged.