this.TaskPaneProcessMap.Visible = false;
May be you need to set the Visible property to true?
Anyway, is your add-in enabled? Did you have a chance to check out the COM add-ins list in Excel? Is it listed in the Inactive add-ins list?
Microsoft Office applications can disable add-ins that behave unexpectedly. If an application does not load your add-in, the application might have hard disabled or soft disabled your add-in.
Hard disabling can occur when an add-in causes the application to close unexpectedly. It might also occur on your development computer if you stop the debugger while the Startup event handler in your add-in is executing.
Soft disabling can occur when an add-in produces an error that does not cause the application to unexpectedly close. For example, an application might soft disable an add-in if it throws an unhandled exception while the Startup event handler is executing.
When you re-enable a soft-disabled add-in, the application immediately attempts to load the add-in. If the problem that initially caused the application to soft disable the add-in has not been fixed, the application will soft disable the add-in again. See How to: Re-enable an Add-in That Has Been Disabled for more information.