open /root/.jwm/jwmrc-personal ,here is my desktops config:
<!-- Number of virtual desktops -->
<Desktops width="2" height="1">
<Desktop><Background type="command">/usr/local/apps/Wallpaper/set_bg /root/Downloads/1.jpg</Background></Desktop>
<Desktop><Background type="command">/usr/local/apps/Wallpaper/set_bg /root/Downloads/2.png</Background></Desktop>
</Desktops>
NEXT,
click menu-desktop-JWMDesk manager,make or not make some changes,then click "apply",the jwm will be reloaded,it will automatically change back to :
<Desktops width="2" height="1"/>
<Desktop><Background type="command">/usr/local/apps/Wallpaper/set_bg /root/Downloads/1.jpg</Background></Desktop>
<Desktop><Background type="command">/usr/local/apps/Wallpaper/set_bg /root/Downloads/2.png</Background></Desktop>
</Desktops>
you can see that "/" in the "<Desktops width="2" height="1"/>"
here is a SOLUTION ,you can edit the etc/xdg/templates/_root_.jwmrc to config your virtual desktops,dont touch root/.jwm/jwmrc-personal.deleted related lines in jwmrc-personal.