Error: A connection must be specified for $Source when using 3.5 LOOKUP function.
An expression in the mapping uses the LOOKUP function and you did not specify a database connection for the $Source Connection Value session property.
On the General Options settings of the Properties tab in the session properties, enter a database connection for the $Source Connection Value property. When you create a session based on a mapping that uses the LOOKUP function, you must specify the database connection for either the $Source Connection Value or $Target Connection Value in the session properties.