disco2 v8 emissions help needed

hi disco just failed emissions on lamba test.
fitted 2 new sensors but failed again.
now going to change the cat and try again.
if this fails what to next.
had complete engine rebuild last year new rings heads , new block etc.
any body come across this same problem.

many thanks

what exactly was the emissions reading?
i did a brand new engine last week with only 100 miles on passed with flying colours

hi changed camshaft sensor as textbook showed camshaft sensor fault.
so far new cata
new lamba sensors
new air mass sensor.
plus new camshaft sensor.
new plugs etc.
starting and running ok but still smells rich.
a bite of black smoke out the back which i did not have before it went on text book.
going to put back on text book see whats going on now.
before going on text book , only problem on emissions was laba reading, co was way down, now local garage checked emissions reckons it worse.
so landrover garage says one think mot gagarge sees somthing else.
what to do next
many thanks