NationalInstruments.TestStand.Interop.API.PropertyObject myArrayVariable = (NationalInstruments.TestStand.Interop.API.PropertyObject)e.uiMsg.ActiveXData;
You can then either use the teststand API to access the individual elements, or, if the array is an array of a basic type, you can do the following:
double[] myArray = (double[]) myArrayVariable.GetValVariant("", 0);
For more help with accessing arrays from .NET see the example: <TestStandPublic>\Examples\AccessingArraysUsingAPI\UsingDotNet\
-Doug