I found some useful information from this link.
http://sqlblog.com/blogs/Aaron_Bertrand/default.aspx?p=7
Here's the info from the link " this could have to do with UAC, or that the domain controller could not be reached, or that the domain account could not authenticate against the log shipping partner, or that the log shipping partner was down. Try changing the service account for SQL Server to a known domain or local account, rather than the built-in local service accounts, and validating that the partner instance is accessible"