I have a web application that uses the Salesforce API to create Contact, Account, Opportunity records. We set up an administrator user with full permissions to use as the Oauth login user, and I use it as an admin for development. I went on vacation so this system admin user was being used for API access only for over a week.

Then all of a sudden the system started returning errors to me (using Django/Python for my client, pasting verbatim) 

SalesforceError: {u'errorCode': u'CANNOT_REPARENT_RECORD', u'fields': [], u'message': u'owner is inactive, cannot reparent record'}

Thing is the owner in this case should be the system user I created and any other records that would have been touched with it are owned by active users. I logged into the SF web interface with my admin user, the errors stopped but I'm not sure if it was related.

My question is - is it possible that the user was flagged as inactive automatically? I can't find a setting that would change this. Would it be caused by something else or am I on the right track?