Tell me a little more.
What software version are you running and is this on a redundant or non-redundant system?
I've only seen this one other time on a Microlight running Q-stream.
It wasn't really a problem with the software. The drive was just plain worn out.
Most likely what has happened to cause this is the drive has acquired a hard error (physical media error or bad sector).
Another possibility is it was formatted with the incorrect LOAD and REDUND partition sizes.
You can always reformat with a LAB1 qualifier, which I think is still valid.
It is as close to a low-level format as you can get and possibly recover.
However, depending on the age of the hard drive, replacement may also be in order. Even the best of them won't run forever and once they start developing sector errors it's usually downhill from there.
Interesting note, I learned recently that even some of the secondary market resellers are starting to steer their customers to "new" Mitel drives versus trying to squeeze more mileage out of used drives.