Help Lost ROOT, can't update, can't reroot

[wow08816]

I have an ATRIX 4G 2.3.4 AT&T 4.5.91. It was rooted at one time but somehow lost its root. I also disabled my BlurUpdater.apk when the phone was rooted to avoid update messages. I am unable to enable the BlurUpdater because I am no longer rooted. So I am trying to reroot my ATRIX to enable my BlurUpdater and are running into problems:

C:\Root>fastboot flash preinstall root.img
sending 'preinstall' (32768 KB)... OKAY [ 4.118s]
writing 'preinstall'... OKAY [ 2.278s]
finished. total time: 6.396s

C:\Root>fastboot reboot
rebooting...
finished. total time: 0.000s

C:\Root>adb shell
$ /preinstall/dosu
/preinstall/dosu
/preinstall/dosu: not found
$ /bin/mount /system -o remount,rw
/bin/mount /system -o remount,rw
/bin/mount: permission denied
$

The /preinstall directory appears to be an empty directory.

Any help is appreciated.
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