For some reason they both open the start menu, and the second one doesn't hide it. At first I thought the buttons might be overlapping, but when I moved the hidetaskbar button away and clicked on it, it still opened the start menu.
What am I doint wrong? Is there a better way to achieve this?
Assuming you are using this version of "openstartmenu.exe", then I would say that your problem is not having that program in the correct path.
Try moving the "openstartmenu.exe" to the same path as your skin file, then try: LeftMouseUpAction=!Execute ["#CURRENTPATH#openstartmenu.exe" /hidetaskbar].
Using the "/hidetaskbar" switch made my taskbar disappear (but left the start button)
Using the "/showtaskbar" switch made my taskbar appear, and opened the start menu.
C:\Users\YourName\My Documents\Skins\MySkins\Plugins, and you are calling it from a skin that is in some other folder in \MySkins like C:\Users\YourName\My Documents\Skins\MySkins\Clock\Clock.ini.
P.S. Just a suggestion, but "plugins" has a specific meaning in Rainmeter, and a whole different folder also called \Plugins that actual plugins are stored in, so I would consider renaming your folder to Utilities or Apps or something else, but that is just a suggestion, Rainmeter won't care a bit, I only worry about confusion going forward.