Modelsim error due to non-globally static expressions

[dinyar]

** Error: ../../hdl/ugmt_serdes.vhd(256): (vcom-1436) Actual expression (infix expression) of formal "iTracksO" is not globally static.
** Error: ../../hdl/ugmt_serdes.vhd(258): (vcom-1436) Actual expression (infix expression) of formal "iTracksF" is not globally static.
-- Loading entity serializer_stage

Leads to failures in the testbench.