Lock a cell based on a specific criteria

At present (you may have seen some of my other posts) I'm creating a timesheet for use by external managers, this means I cannot use VBA as many are not able to use macros on their systems.

As a result I'm trying to be able to lock down data entry on specific cells (on the Manager Entry tab) based on whether or not the person selected in cell B5 then has the allowed type of overtime on the Source tab.
I've attached an example if it is of any use.