This dialog is to advise the user that the application they are about to use may not be aware of square screens or screen rotation, and may not display properly in landscape mode. This dialog will only appear if the VersionMin value (which specifies the lowest OS revision number your app supports) file is less than 4.21.
Since setting VersionMin to 4.21 will prevent your application from installing on older Windows Mobile-based Pocket PCs, it is recommend that you disable this warning message by setting the BuildMax value (which is typically unused) equal to the following values in Table 2:
Table 2. BuildMax values
0xA0000000 Application supports square screens (240x240 pixels).
0xC0000000 Application supports screen rotation.
0xE0000000 Application supports square screens and screen rotation.
These parameters can be changed by editing the [CEDevice] section of the INF file which cabwiz uses to generate your CAB file. For more information on the INF file format, please consult MSDN documentation.