After upgrading to 8.2 (luckily we're not live on this yet), I needed to update the service account password I use to connect to AD and ran into this same issue, but only on Lifecycle Manager's Identity and Tenant Management. It updated fine in Identity Manager's Identity & Access Management.
My question is, if it gets changed in Identity Manager, does that change propagate to Lifecycle Manager? I ask because even though my Test Connection failed in Lifecycle Manager, my actual Sync in Lifecycle Manager didn't. Is this error LCM's way of saying "Go change it in IDM and I'll be fine"?