When I move a fractional dual dimension, the fraction drops down through the dim line.  How do I correct this?  I am using Autocad 2010

You'll have to adjust the spacing between the dimension itself and the line it sits over.  This can be done in individually via Properties or globally in your dimension style.

Other possibilities in Dimension Style options:
1.  Reduce the Text's "Fraction Height Scale" [the height of the numerator and denominator text as a proportion of the main text].
2.  Change the Primary Units' "Fraction format" from "horizontal" [assuming that's what you're using -- it would make the tallest fractions] to "diagonal," or maybe even to "not stacked."