Generally speaking, you can check the social post's reporting page, and simply scroll down to where the error's messaging is, or click the banner at the top of the errored post's reporting page. A lot of these can be as simple as disconnecting and reconnecting the page that errored, since the errors are typically caused by API connection issues. Sometimes, such as with Instagram accounts, if they're changed to an incompatible page type (like a Creator account for Instagram) after they were connected to your Constant Contact, it may require updating the page's settings on the native site.
For parent partner accounts, it may be a bit different. Did you receive a notification or anything that specifically named the social post, or includes the child account's owner name, username, or email in it? Or anything that indicated the errored social page's specific name? It may be easier to call or email Partner support, since they'd be better equipped to troubleshoot from within your account, since general support can't do that parent partner accounts.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ William A Community & Social Media Support