suppress the component in assembly those have no effect try to do simulation only on the required components not with whole assembly its a general rule applied in all fea tools restrain ur component properly and please dont try to do simulation on whole trailer assembly just take the structural member
Those errors are related to poor element quality, i.e. negative jacobian values. You probably have some bad geometry, very small features, or are trying to use too large of a mesh size. Have a look at your geometry for errors, use local mesh refinement, or reduce your mesh size and try again.