0xEA8 is a rather low number. A read violation that close to 0x0 usually means that a function is being called on a nullptr object.
In e.g. your 'gui.get<tgui::Button>("USR_Button")->setText(User);' line, are you certain that "USR_Button" exists and is a Button type? Otherwise 'gui.get<tgui::Button>("USR_Button")' would be a nullptr.
If you run the code with a debugger it should tell you exactly where it crashes. If the location isn't in your own code, you should be able to show a call stack that will tell you exactly where it happened.
In e.g. your 'gui.get<tgui::Button>("USR_Button")->setText(User);' line, are you certain that "USR_Button" exists and is a Button type? Otherwise 'gui.get<tgui::Button>("USR_Button")' would be a nullptr.
If you run the code with a debugger it should tell you exactly where it crashes. If the location isn't in your own code, you should be able to show a call stack that will tell you exactly where it happened.