3d laminar flow - solver problem: Segregated group 1.

Hi

I´m simulating the convection heat transfer in a pipe. The external surface of the pipe receive solar radiation to heat the fluid that is flowing.

I start my model with the laminar flow and after I can validate this part of my model I'll put the heat transfer in the pipe to the fluid. But some problems ocurred when i started to comput my model.
When I selected the inlet boundary condition to "velocity" I obtained successful simulation with initial velocity field "0". When change the initial velocity field the simulation dont converge. I dont understand this.

I have changed the inlet boundary condition to "laminar inflow - flow rate", because in the real model I have just the values of fluid flow. At the first time that I tried to simulate occured the following error : "Segregated solver steps do not involve all components." So I added the variables in the segregated step and now the following error is occuring in the simulation:

Failed to find consistent initial values.
Segregated group 1

Matrix has zero on diagonal.
Last time step is not converged.

I dont understand why this error is occuring. I tried to change the initial values but the error persists.
Can someone help me? I put my file in the attach.

Another thing I would ask is how to plot the velocity profile along the pipe?

thanks.

Gustavo