Can a _contact_ become corrupted?

I have one contact (I hope only one, at least!) to which I cannot always add notes. Frequently when I do an error appears:

"The command cannot be completed because an unexpected error occurred."

I also can't delete notes that are attached to this contact.

One option I haven't explored would be to rebuild the contact and add the notes all over again. I haven't taken the time to see whether this would solve the problem.

Does anyone have another suggestion? Thanks for your help.