Windows does not allow pinning shortcuts/programs to the taskbar that contain certain words. From the MSDN article Application User Model IDs (AppUserModelIDs):
You can work around this by first creating a shortcut to isdev.exe (do not include any of the above words in the shortcut name). This shortcut can then be pinned to the taskbar.
If any of the following strings, regardless of case, are included in the shortcut name, the program is not pinnable and is not displayed in the most frequently used list:
Josh Stechnij - Software Engineer - Flexera Software: InstallShield Team