Macro fails to open form

I have a macro that creates a drawing based on the dimensions I type into a form. It worked fine in Windows7 64b, but now on windows 11 it fails to load the form, This is the code that calls the form

Sub CreateUnit()
    UnitDimensions.Show vbModeless
End Sub

Is there anything I can do to make it work in Windows11?  FWIW My other macros are working fine as far as my testing to date has proven, but this is the only one that uses an input form

TIA