That oil light is very worrying.

Especially since it didn't come on before.

It sounds as though your getting low oil pressure at idle. (do not run the bike until you can confirm this isn't happening as you'll get engine damage)

Maybe oils getting too thin!?

10/40 is the correct grade synth or semi synth (semi synth is prefectly ok) if there the same grade they should behave the same.

Is the oilstraner clear? (its in the sump) and nothing blocked?

Perhaps draining the oil has moved some crap in the engine?

i would be sus of the oil filter

hi
did a test started bike no oil light on as it warmed up oil light came on as the temp rose the revs needed to keep the ligth off rose from 1500 rmp to 3000rpm

you could hold the revs at 2000rpmand after a wile the light came on so increse the revs to 2500rpm all ok but after a time oil light came on

it didnt do it when the oil was first put in
off to find a pressure switch new oil and filter
any other idears

thanks for the replys