This sometimes happens with Windows. Usually a reboot will solve the problem. However if this doesn't, try setting the icon for the shortcut(right-click pinned icon, right-click program, left-click properties, select "change icon...") or refreshing it by switching to a different icon, applying it, and then reverting back to the original icon. Remove the shortcut from the taskbar and replace it with the start menu shortcut or simply drag the .exe file to the taskbar.