tgui::GuiSFML was from TGUI 0.9, in TGUI 0.10 you can just use tgui::Gui.
Edit: Popup example seems to be the only one still using GuiSFML, I'll fix that line too. (The "GuiBase" has been updated on the website in the meantime, but the old version is still in some caches).
Edit: Popup example seems to be the only one still using GuiSFML, I'll fix that line too. (The "GuiBase" has been updated on the website in the meantime, but the old version is still in some caches).

