i have had the same problem,even with the pmdg737 for fs9 when using a star into my local airport, if i used rc4 atc always started my descent approx. 45miles before the tod that the fmc had calculated i always flew the star perfect, sometimes i only selected the star and left out the runway and only selected a runway when i was almost at the final fix on the star this worked ok as well. sometimes a approach is ok and sometimes i have to go into the legs page and modify the waypoints so i can fly the star.

Sometimes just wind changes can cause that. Say if you are descending at 1500 fpmwith a certain wind and at say 280 knots IAS. Then the wind changes direction, andall of a sudden you are doing 290 IAS. The VNAV will naturally pitch up to slow theplane down, and in doing so the descent path will change due to the more shallowdescent. It can then give you the FMC notice. But in a case like that, it will usuallygo off once the speed stables, and the plane resumes the previous rate of descent,and thus recalculating that you can indeed make the descent. Naturally this willshow up more when the wind is lively and changing direction a lot.Of course, some times you will end up needing to modify the descent in ordernot too end up too high near the airport. IE: if you picked up a strong tailwindall of a sudden, etc.

It's not a wind problem. Most of the Sydney STARs in the Navigraph database do not terminate in vector legs, but simply cause a discontinuity to be created. You cannot remove this discontinuity because there is nothing to join it onto (unless you draw the circuit with PBDs). The work around is to insert an altitude constraint at SY/VOR for 6000FT/9000FT (depending on direction) and update as advised by ATC. You will still receive messages such as "no descent path after SY", but that's okay. Once you are on downwind, descend as required to be at ~4000FT on base for 10NM final. If ATC have to extend you further you may need to level off.