The DynamicBackColor needs an expression it can execute for each row of the cursor / table so it needs to be a charicter expression.

See help on DynamicBackColor - ex.
frmMyForm.grdGrid1.SetAll("DynamicBackColor", ;
"IIF(MOD(RECNO( ), 2)=0, RGB(255,255,255) ;
, RGB(0,255,0))", "Column")