When Xfce starts up the plug in is not visible in the panel. opening and closing the preferences dialog for the plug in makes it reappear. restarting the panel makes it vanish again.
Created attachment 3646 Patch to fix start bug of xfce4-genmon-plugin I use this patch to fix this bug. It don't seem cause other problem, but use for few time.
I confirm that this patch fixes the display on restart issue of genmon with no other issues.
Nice! It's been a while. I recommend this to be merged and gets included by the repository maintainers. For "normal users", this plugin has been broken for two releases of Ubuntu now. And it's a shame to download 100 MB of libs and build-deps to fix this kilobyte plugin. Anyway, for people going to fix the plugin: (x)Ubuntu 11.10 does not have the required libxfce4panel-1.0, deps can be found in xfce4-panel-dev instead. :)
It looks like the call to SetTimer() at this place was removed when the patch in https://bugzilla.xfce.org/show_bug.cgi?id=4050 was applied (the rationale was: "This patch also eliminates a spurious update when the plugin is initialized but there is no command configured. This update caused "XXX" to be displayed in the panel").
Fixed in Git: http://git.xfce.org/panel-plugins/xfce4-genmon-plugin/commit/?id=78e457ae136015a7cc2260bb4e95cc14307f450e
Fixed in 3.3.1.
*** Bug 7527 has been marked as a duplicate of this bug. ***