Note that the default layer numbering sequence in APPX 5.1 is different from that in 5.0, where they were 3, 2, and 1 rather than 30, 20, and 10. If a screen was defined in APPX 5.0 where some widgets had @SLN specifications and others did not, that screen may very well not display correctly when viewed with a 5.1 client.

The 5.1 client has a preference setting (last item under Options) called "oldLayerNumbers" which can be turned on to use the pre-5.1 layer numbers. This flag should be set to "true" for any user who is connecting to an application that relies on the 5.0 layering scheme.