Default [Q] Cyanogenmod (official) OTA update failing - root possibly lost?


I've been prompted in the last few days to install an OTA cyanogenmod update.

When I accept the installation, the phone reboots.

About 1/5 of the way through the progressbar, the installation halts and I come to a screen headed "Root access possibly lost. Fix? THIS CANNOT BE UNDONE".

Various 'no' options, then 'yes - fix root (/system/xbin/su). Regardless of whether I select yes/no, the installation seems to fail and I reboot into my current version.

Lower on the screen, after the heading "Installing update...." is the error code "assert failred: apply_patch_check("/system/xbin/su", [hexcodes], [hexcodes]) E:Error in /cache/cm-maguro-[hex]" (Status 7) Installation aborted.

Any views as to how I can get past this and get the update installed?

Many thanks