Vlookups In VBA

I have an array (partArray) that contains a number of parts that I need to get values for. The part array is populated (Thanks Norie!) by bring in the contents of a cell and splitting them into array elements. I then run them through a trim loop to remove the white spaces. Up till here thefunction works fine.

I created a partRSL array to hold the matching value for each part ( I know i can use multidimensional arrays but i dont understand them yet and need to deliver a prototype to get some approval from senior mgmt ).

The idea is that as we run through each element of the partArray we will vlookup the corrseponding value and assign it to the appropriate element of the partRSL.
When I use the function below it returns a #value. I think that the element of the partArray i want to lookup is not being used as a string and so the lookup is failing.
As a test to see that this is working i have the function returning the value of element 0 in the partRSL array as it is distinct from the rest. (It should be returning a number (integer)

Function FindAlt(option_address)
' Initialise the array
Dim partArray() As String
Dim partRSL() As String
Dim i As Integer

'Populate Array by spliting the comma separated contents of the select cell and assigning each to an array element
partArray = Split(option_address, ",")

'This works fine
For i = LBound(partArray) To UBound(partArray)
partArray(i) = Trim(partArray(i))
Count = Count + 1
Next