Disable visual themes for Gui4Cli program on Windows 7 (64 bit)

Hello,
I try to disable visual themes for one of my programs using uxthemes.dll but can't get further ... not even sure that the dll gets loaded ($$func.ret always = -2147024890).
Sample code:
------------------------------------------
G4C DisableVisualThemes
xOnload
SysDll Declare uxtheme SetWindowTheme int "int/pstring/pstring"
say "The declare uxtheme SetWindowTheme function returned: $$func.ret"
call uxtheme SetWindowTheme 0 "" "" // Disable visual themes
say "The call uxtheme SetWindowTheme function returned: $$func.ret"
// SetWinAttr #this background color "150/150/150" // gray
// Change the xCalendar colors and set preferences
Use Calendar #this calendar_id
Calendar color back "250/150/0" // orange
Calendar color bkmonth "250/150/0" // orange => does not work if themes enabled ?
Calendar color text "0/0/0" // black
Calendar color bktitle "255/0/0" // red
Calendar delta 1
GuiOpen #this
xOnClose
SysDll Free uxtheme
say "The Free UxTheme function returned: $$func.ret"
GuiQuit #this
Window #CENTER #CENTER 300 250 "Disable Visual Themes"
xButton #CENTER -40 -10 30 "Close"
GuiClose #this
xCalendar #center 10 200 180
Attr id calendar_id
Attr style week;Attr frame sunken
------------------------------------------

If it works, it should display the background color of the calendar in orange (as set above with 'bkmonth').

Does anybody has a clue what I am doing wrong here?

Any help is very appreciated.
Best Regards, Rene




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