Error "You cannot select server instance with engine lower than 5.1 as subscriber if publisher is 5.1" appears when setting up Log Shipping. Publisher and Subscriber are same when xp_sqllitespeed_version is run. Publisher and Subscriber are the same when xp_sqllitespeed_licenseinfo is run. The LiteSpeedLocal.LSVersion.LSOptions is the same on Publisher and Subscriber.
Permissions between Publisher and Subscriber
1. Verify the SQLServer and SQLAgent logon account password. It may have changed and failed to connect.
2. Setup an alias with the correct port and connect via the alias.
3. Use a UDL connection test on the subscriber side to verify you can connect to the instance from your operating system.