Hi,it's may be some things.
1. May me you handly define very small mesh size.
2. Your model consist of too much small complex element or models size is greater than 1000 wavelength...
3. Your model consist unfinded collision
It may be your meshes size are very small and Hfss needs very large space on your disk to simulate.
when simulating see your free space on that drive.
be successful
yeah, i having the problem too and all free space on my drive are consume when simulate with more numbers of adaptive passes. I found out that the hard disk space (up to gigs size) that used by HFSS fail to restore and now a warning message "low disk space" always displayed when i start my pc. Anybody can suggest some ways to get back the hard disk space?