Lookupvalue value error

Anonymous ,

I checked your screenshots.
Second image means that there is no unique value for parameters that you use in lookupvalue function. It means that you should add some more parameters which will return unique value.
First image, the logic is to return max value per some criteria. Currently your return value is [Dealer Code] and you are searching max dealer code per dealer code [allexcept(dealer code)]. So it will not find unique values.

So here are steps:
In first image, first parameter is min value that you want to return per specific criteria. And criteria should be inside AllExcept function (AllExcept means group by: so you will get some value per criteria1, criteria2, criteria3..).
In second image make sure to have as many lookup parameter as needed to make sure you have unique value to return.