I compiled your 24U Plug-In Template 3.1 with Visual Studio 2012. The
FMPluginDebug.fmx loads and works fine on all Windows Vista, 7 or 8
computers I have tried with FileMaker 12.
On all Windows XP SP3 computers, the FMPluginDebug.fmx never shows up in
the Plugin panel of Preferences dialog when placed in Extensions folder
and restarting FileMaker.
Is this a known problem? Is there a work-around?
Early versions of Visual Studio 2012 didn't have target support for Windows XP. You had to install Visual Studio 2010 alongside.
More information can be found here (for example):
That's why our template still comes with the Visual Studio 2010 project.
We recommend to install Visual Studio 2010 and use VS2010 project from the template in VS2010 mode inside Visual Studio 2012.