Polysurface denies trim

Hi,
V5
I see I have a polysurface, result of a kind poster fixing a problem I had.
I need to trim away the part ABCD having lowered the trackway floor, but despite selecting floor and walls and using to trim, that area wont trim.
Also this polysurface is denying use of MoveEdge without causing strange effects underneath (another post)

is there a convert polysurface to normal surfaces which do behave ?

I am not used to surfaces denying normal tools usage.

I am unable to explode it.

polysurface denies trim.3dm (593.9 KB)

Cheers

Steve

Seems to work for me.
trimx.3dm (107.3 KB)

Select the Cyan surfaces and trim the orange polysurface in two places.

Hi Jim,
Heartfelt thanks for replying so soon,
that works for me,
I have a sneaky feeling I forgot the 2nd vertical wall !

Cheers

Steve