Vista - BitLocker reports "an error occurred" during login

This past week, I've noticed that when I log in, Windows reports an error in
the system tray via a tooltip. The tooltip's title is "an error occurred"
and the descriptive text indicates that errors were detected on the disk and
that chkdsk should be run.

I ran chkdsk /f on my C drive, and the next time it rebooted, it indicated
that no errors were detected.

Still, each time I boot up, this error appears, but it usually is only there
for half a second, maybe even less. It's almost like the system is issuing
the error and then suddenly "withdrawing" it as if everything is okay. But
today I sat waiting for it, and as soon as it appeared, I immediately
double-clicked on the icon before it could disappear. A dialogue appeared.
The dialogue title was "Windows BitLocker Drive Encryption."

The dialogue indicated that errors were detected on the disk and that I
should run chkdsk /r (not /f, but /r (full surface scan)) and that if after
running that and the error persisted, there was a hardware fault.

I've been running BitLocker for weeks without fuss or trouble, so why would
there suddenly be a "hardware fault."

I checked the System and Application event logs. There is NOTHING posted by
BitLocker in either log indicating a problem. Furthermore, whenever disks
start to develop bad sectors, you see the dreaded errors posted by "disk"
that indicate bad blocks were detected. Other events are often posted by
dmio or ntfs, again indicative of disk and/or controller issues. There are
NONE of these.

I have two external drives attached, both via USB, that are also encrypted
with BitLocker, thanks to the command-line interface manage-bde.wsf. I
regularly boot up with these drives attached and I don't unlock them until
after I log in.

Is it possible that BitLocker is raising the error for one of these external
drives and not the internal laptop drive? Is it maybe because the drives, by
default, show up as RAW (since they're "locked" until I use either the key or
password to unlock them)?

Best regards,
Matt