I recently tried to deploy some changes between sandboxes using the Force.com migration tool and got the following error:
Failed to process the request successfully. Cause(ALREADY_IN_PROCESS): null: The changes you requested require salesforce.com to temporarily lock your organization's administration setup. However, the administration setup has already been locked by another change. Please wait for the previous action to finish, then try again later.
According to this question, the organization can be locked by deployments (of course) or during unit tests (seems odd to me, never seen it before). Regardless, neither of these is happening in the org I am working in. Is there documentation somewhere that lists all potential causes of an organization lock?