Compaq CQ56-154CA Wlan failed to connect after SP1 upgrade

Compaq CQ56-154CA laptop Windows 7 Home Premium SP1.
I Upgraded to SP1 and wlan won't connect.
I restored to previous restore point and was not able to resolve the problem even by reinstalling the original HP driver.
I re-installed Windows and all was OK.
I upgraded to SP1 again after a few days and wlan failed again.
The wlan network driver is the correct one RTL8191SE by Realtek Semiconductor Corp.
The wlan icon does not display an exclamation mark.
The light on the wlan indicator displays white so power is on.
This laptop is a dual-boot with Linux/Ubuntu 11.04 and the wlan is functional.
Is it possible that SP1 replaces the existing driver with a Microsoft driver?
Lots of help needed; reinstalling Windows 7 is very time-consuming.
I have resorted to a wired network with this laptop - how retro can it get...?

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