I think I found a bug when trying to convert a game from wbfs to wia with the argument --compression FAST. GOOD and BEST seem to work!
!! wit: ERROR #25 [CAN'T OPEN FILE] in SetupWriteWIA() @ src/lib-wia.c#2371
!! Can't open file stream: /Users/me/Desktop/hjk.wia
!! -> Bad file descriptor [9]
2012-11-06 15:02:36.589 Witgui[6805:303] !! wit: ERROR #41 [FATAL ERROR] in write_data() @ src/lib-wia.c#1483
!! ASSERTION FAILED !!!
!! wit: ERROR #25 [CAN'T OPEN FILE] in SetupWriteWIA() @ src/lib-wia.c#2371
!! Can't open file stream: /Users/me/Desktop/hjk.wia
!! -> Bad file descriptor [9]
2012-11-06 15:02:36.589 Witgui[6805:303] !! wit: ERROR #41 [FATAL ERROR] in write_data() @ src/lib-wia.c#1483
!! ASSERTION FAILED !!!