Actually you do need tablet pen for the brush tool and the vector pen tool. The mouse works if you don’t have a tablet or if you have a tablet but didn’t use the tablet pen. After you use the tablet pen, the mouse no longer works with these two tools. It is a bit strange yes, but this was done to fix issues with tablet drivers I got. (Not all tablet signals were received by application and in some situation I couldn’t tell if the pressing signal comes from the mouse or from the tablet pen, which is needed for getting the correct pressure).