Hi,
I don't have those tables, so couldn't run the script.
but try to change
AND mwebMatrix.Mat_Date >= Currency.FX_Start_Date (+)
AND mwebMatrix.Mat_Date <= Currency.FX_Finish_Date (+)

to AND mwebMatrix.Mat_Date between
nvl(Currency.FX_Start_Date ,mwebMatrix.Mat_Date )
and nvl(FX_Finish_Date ,mwebMatrix.Mat_Date )

u can use the same creteria in <= or >= conditions?

try this and see if it helps u!!
-venu