Just replying here to offer my own solution (after all the other ones in the thread didn't work for me).
It's certainly odd, but I'm using a (very) old version of Android which doesn't have most of what the guys here have. It's a phone simply intended to be a phone, so there's no Internet access.
Anyway, when I went to all of my apps, I deleted all of my data for both the Contacts and Contacts Storage apps, and then forced them both to stop. Then, I opened up the Contacts app again to restart it, and the error stopped occurring.
I've had this issue in the past as well, where sometimes certain numeric combinations might've been saved as an erroneous contact, causing Contacts to misbehave. But that time, a full reset fixed it.
Certainly YMMV, but if you don't mind spending some time to backup your contacts list, give it a shot.