Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
improsper (inpr-), spĕra, ĕrum, adj. [2. in-prosper], unfortunate, unprosperous (post-Aug.): fortuna, Tac. A. 3, 24: moles insidiarum, id. ib. 14, 65: multa claritudine generis sed improspera, id. ib. 4, 44.
Adv.: improspĕrē, unfortunately: cessit, Col. 1, 1, 16; Tac. A. 1, 8; Gell. 9, 9, 12.