Error: Cannot evaluate expression

Hi all,

I keep getting this error when trying to compute the study on heat transfer:

Failed to evaluate variable.
-Variable: mod1.nitf.U
-Geometry: 1
-Domain: 3
Failed to evaluate expression.
-Expression: mod1.nitf.U
-Plot:slc1 (Slice)

The study computes and the temperature plot is generated, but the velocity plot fails.

The error and the model are attached.

Please help!

Much thanks!

Idan