[Moved]: HFSS adaptive passes happens sometimes, and ...

I am working on HFSS designing of patch antenna. Here in the design when it is simulated it sometimes completes adaptive pass and does the analysis but the same design if I close and open and re validate and run then it shows conversenge problem. Again if I save the file in some other directory then sometimes it passes sometimes it doesnt.What is this problem all about?
Also even when it passes S11, vswr all are good but the Z0 plot in smithchart just shows a dot. Please help me if you have any idea about this