I set up volume.1. of 45*35*20, and split it with 9 of small cubic volume(5*5*5), which are inside volume.1. Then I did mesh on volume.1. and there is error like: 'Cannot submap volume.1. Further decomposition may help. Also check interval assignments for correctness. ' What can I do for decomposition?

btw, I tried split with 6 of cubes(also 5*5*5). Mesh can work on volume.1.

You should try a different meshing type.