I'm not sure which parameters line you are referring to Ron, but its obviously wrapping your entry into one big string.
You might get it to work like lookfld= ' & Cls:Dx1 & '
note the single quote at the end
that will take the 'lookfld=' as a literal, then the value of the variable and a single quote as Bruce will add a single quote to the end of your expression, so it will add a nothing to the end
In the module you should go to "Source" and find lookfld=
You will see how NT8 is constructing the expression.
K