Log shipping on secondary server
I've ran into this same problem! As Mr. Vernon stated, the account needs admin access to the server.  However, that is not the recommended way of providing access to the service account, especially if you're to follow the "least privilege" security mantra.

Instead, perform the following:


Create an appropriately named security group
Add the SQL Server Agent account to the group
Create a shared folder on the server you're shipping the logs to
Assign the newly created security group with Modify permissions to the folder