Problem uninstalling a font from Windows 7 "Control Panel"

when I try to uninstall a font I installed (only light style)

the system throws me a window that says ... "The file can not be uninstalled by being used, close all programs and try again"

the problem is I do not have any open program and also took a couple of days without being able to uninstall this file .OTF

hope you can help me, thanks!