Mesh Problem

Hello,

I have problem with mesh generation for my model. I made a 3D glass beads with lots of grains.
When I want to mesh that I faced some error in meshing. sometimes it meshed but then during study meshing makes a problem: (Failed to generate mesh for domains :...)
I spent lots of times to figure out the problem, but no success,
I would appreciate if any body could help me.
Thanks,
Saeed