need help URGENTLY! inverted mesh warning when applied fluid-structures module

Hi all,

I'm facing inverted mesh problem when using fluid-structures model.
I had model two "particle" and set channel as moving mesh.
However, the simulation stop with huge inverted mesh warning and error below.

"Recoverable error in residual, but solver could not recover.
Time : 3.982005826471095
Last time step is not converged."

Can any one suggest any solution to this problem? I had attach my file in this thread.

Thanks