Its checking for a file in the directory with the same name, before it creats a wblock.
(IF (not (= (TYPE (VL-FILE-SYSTIME (strcat blockdir "\\" newb))) 'LIST)) (command ".wblock" newblock "" point "l" "" "oops") (princ "\nBlock name already exists in 'Blocks' directory.")
)
(IF (not (= (TYPE (VL-FILE-SYSTIME (strcat blockdir "\\" newb))) 'LIST)) (command ".wblock" newblock "" point "l" "" "oops") (princ "\nBlock name already exists in 'Blocks' directory.")
)