raid 1 partition lost after rebuild

Hello...

I have a computer with an Asus MB which has a built-in SIL3114 sata-raid
interface. I use it in raid 1 mode, having 2 mirrored disks. Primary
partition is C, system, and secondary partition is E, files.

OS is Windows Server 2003 SBS.

It's been running well for 2 years, until it started recently to produce
Blue Screens Of Death, which I tracked down to a problem with the raid array.

At boot time, I can access to a raid control panel, which told me something like :
- disk 1 : CURRENT
- disk 2 : rebuild

In the main menu, there is an option to "rebuild raid1 set", so I took my chance...
The thing said "copying" (I assume it was copying "current" onto the other)...
It rebooted and...

MISERY ! The "E" partition was empty. All my files vanished ! The partition
was there, but empty. Partition "C", though, was intact.

Can someone explain me what happened ? Why E was wiped, and why C wasn't ?

Well, the Blue Screens have dissapeared, and I had a backup for E, so, no
great panic, but, still, WHY ? HOW ?

I'm having a hard time finding correct information about raid diagnostic, and
especially what to do in case of a failure... SIL, which is the main source
for affordable raid interfaces documents quite badly its products... (when
it's documented at all). I'm slightly frightened of what could happen and
what could I do in a more critical situation...

Fabien.