transmission problems, push rod won't push

I was changing the chain and sprockets on my 88 ZX10 this weekend. This
involved pulling the hydraulic clutch slave cylinder from the sprocket cover
prior to pulling the sprocket cover. After reassembly my clutch won't work.
At first I thought it was the piston getting jammed in the slave cylinder
but when I observed it's action while removed it seems fine. But when I put
it back together it won't disengage the clutch. It seems like the pushrod
won't push in. I can move the pushrod around so it's not jammed but it
doesn't seem to allow the clutch to disengage. Any ideas what's going on?

tia
d