I have had that error to. do you currently run "auto backup" for my contacts backup? I guess I "solved" the problem by turning the auto feature off, and then doing the following:
menu - settings - applications - manage applications - my contacts backup - force stop.
Obviously we shouldnt be getting error messages, yet this is a way to stop them from happening without knowing why exactly. I know we should be able to run MCB when we want, so I'll post when I know more.