BGP unsupported capability code

I recently implemented BGP graceful restart capability in a
custom BGP
app and encountered the same notification.  By looking at
the
capabilities being advertised by the router, and advertising
various
subsets of those capabilities, I narrowed it down to the
MPLS
capability.  It turned out the router deemed MPLS capability
as a
prerequisite for graceful restart.  Adding the MPLS IPv4
unicast
capability to the OPEN message along with the graceful
restart
capability fixed things for me.

Hope this helps.
- Mike