There can be various reasons.
1. Ribbon Creator can only process XML files generated by Ribbon Creator.
btn = Button
tgb = ToggleButton
lbl = Label
cbx = Checkbox
ddc = DropdownControl
sep = Separator
ebx = EditBox
gbt = ButtonGroups
mnu = Menu
sbt = SplitButton
gal = Gallery
cmb = ComboBox
2. Ribbon XML must be well-formed. (Try to open the file using Internet Explorer.)