DestroyMenuStyle * Fvwm   ##これエラーになる。
MenuStyle * Fvwm

ログを見るとエラーが出てる。

 CMD_DestroyMenuStyle: cannot destroy default menu style. To reset the default menu style use
  MenuStyle * fvwm, Foreground black, Background grey, Greyed slategrey, MenuColorset, ActiveColorset, GreyedColorset

MenuStyleをいじっていたので、どこでエラーがでるのかこのエラーメッセージだと分からないんだな。試してみて分かったのが、DestroyMenuStyle * Fvwmであった。そもそもDestroyMenuStyle * で エラーがでる。デフォルトのメニュースタイルは、Fvwm, Mwm, Winが用意されているが。これはDestroyMenuStyleできませんよ、ということですな。

Fvwm, Mwm, Win reset all options to the style with the same name in former versions of fvwm. The default for new menu styles is Fvwm style. These options
       override all others except Foreground, Background, Greyed, HilightBack, ActiveFore and PopupDelay, so they should be used only as the first option
       specified for a menu style or to reset the style to defined behavior. The same effect can be created by setting all the other options one by one.

       Mwm and Win style menus popup sub menus automatically. Win menus indicate the current menu item by changing the background to dark. Fvwm sub menus
       overlap the parent menu, Mwm and Win style menus never overlap the parent menu.

       Fvwm style is equivalent to !HilightBack, Hilight3DThin, !ActiveFore, !Animation, Font, MenuFace, PopupOffset 0 67, TitleWarp, TitleUnderlines1,
       SeparatorsShort, TrianglesRelief, PopupDelayed, PopdownDelayed, PopupDelay 150, PopdownDelay 150, PopupAsSubmenu, HoldSubmenus, SubmenusRight,
       BorderWidth 2, !AutomaticHotkeys, UniqueHotkeyActivatesImmediate, PopupActiveArea 75.

       Mwm style is equivalent to !HilightBack, Hilight3DThick, !ActiveFore, !Animation, Font, MenuFace, PopupOffset -3 100, !TitleWarp, TitleUnderlines2,
       SeparatorsLong, TrianglesRelief, PopupImmediately, PopdownDelayed, PopdownDelay 150, PopupAsSubmenu, HoldSubmenus, SubmenusRight, BorderWidth 2,
       UniqueHotkeyActivatesImmediate, !AutomaticHotkeys, PopupActiveArea 75.

       Win style is equivalent to HilightBack, Hilight3DOff, ActiveFore, !Animation, Font, MenuFace, PopupOffset -5 100, !TitleWarp, TitleUnderlines1,
       SeparatorsShort, TrianglesSolid, PopupImmediately, PopdownDelayed, PopdownDelay 150, PopupAsSubmenu, RemoveSubmenus, SubmenusRight, BorderWidth 2,
       UniqueHotkeyActivatesImmediate, !AutomaticHotkeys, PopupActiveArea 75.