RE: Warning or Error on Putting Item Into Fixed Location
I don't think there is a way to configurate a warning.
But what you could to is have the mobile device item with Movement by template.
In the work template you select a specific work class which only has specific location types.
The locations which are used for fixed locations should have a location type assigned which is not available in the work class as Valid put location type.
In this way when they try to put stock on that location, they will get an error about a non valid location type.
Hope that helps..