The plan he desperately came up with was rejected, and the book he painstakingly wrote won't sell. Yamashita has hit a wall on all sides.
Literal
Desperately thought-up plan [topic-は] rejection, wholeheartedly made book [topic-は] not-selling. Yamashita [topic-は] all-directions-blocked state [to-に] fallen-into.
八方塞がり is a vivid idiom meaning 'blocked in all directions, completely stuck.' 必死で考えた ('desperately thought up') and 一生懸命作った ('painstakingly made') show the effort that went to waste. 陥っている uses ている for a resulting state. A narrative about professional frustration.