Manipulating a Plot of a FittedModel

Question

I am trying to manipulate a data set and view a dynamically updating plot of the nonlinearmodel fit of the data. The comments in the example code below show the two things that work (manipulating a listplot of the data, and plotting a nonlinearmodel fit) and my attempt to be able to manipulate the data set that generates the nonlinearmodel fit.

data = ImportString["\t16\t13\t9\t6
   600\t2.36\t2.34\t2.31\t2.27
   592\t2.68\t2.61\t2.55\t2.45
   584\t3.66\t3.41\t3.21\t2.93
   576\t4.58\t4.11\t3.81\t3.33
   568\t3.91\t3.61\t3.39\t3.05
   560\t3.62\t3.38\t3.19\t2.91
   552\t3.91\t3.61\t3.38\t3.04
   544\t4.41\t4.01\t3.72\t3.27
   536\t4.31\t3.93\t3.65\t3.23
   528\t3.75\t3.48\t3.28\t2.98
   520\t3.27\t3.09\t2.96\t2.75
   512\t3.10\t2.96\t2.85\t2.67
   504\t3.11\t2.97\t2.85\t2.68
   496\t3.17\t3.01\t2.89\t2.71
   488\t3.25\t3.08\t2.95\t2.75
   480\t3.37\t3.17\t3.03\t2.82
   472\t3.56\t3.32\t3.16\t2.91
   464\t3.83\t3.55\t3.35\t3.04
   456\t4.25\t3.89\t3.63\t3.24
   448\t4.84\t4.47\t4.09\t3.55
   440\t5.70\t5.52\t4.87\t4.11
   432\t10.00\t5.72\t6.10\t5.13
   424\t10.00\t6.18\t5.79\t5.43
   416\t10.00\t5.63\t5.87\t5.72
   408\t10.00\t6.21\t5.73\t5.54
   400\t10.00\t6.19\t5.44\t5.47", "TSV"];

xValues = {16, 13, 9, 6};
(*This works to manipulate the data set and plot the individual \
points*)
Manipulate[
 ListPlot[{Partition[Riffle[xValues, Drop[data[[Upper]], 1]], 
    2]}], {{Upper, 10}, 1, 26, 8}]

(*This works to create & plot a fit for a certain set of data*)
nlm = NonlinearModelFit[
   Partition[Riffle[xValues, Drop[data[[10]], 1]], 2], a*x^b, {a, b}, 
   x];
Plot[nlm[x], {x, 0, 20}]

(*This does NOT work to create & plot a fit for a manipulated set of \
data*)
Manipulate[
 Plot[NonlinearModelFit[
    Partition[Riffle[xValues, Drop[data[[Upper]], 1]], 2], 
    a*x^b, {a, b}, x][x], {x, 0, 20}], {{Upper, 10}, 1, 26, 8}]

The final Manipulate command gives the errors:

General::ivar: 0.0004085714285714286` is not a valid variable. >>

General::ivar: 0.0004085714285714286` is not a valid variable. >>

General::ivar: 0.0004085714285714286` is not a valid variable. >>

General::stop: Further output of General::ivar will be suppressed during this calculation. >>

Any suggestions? Thank you!