daveo61,
You may have sorted this out by now. The syntax is wrong.
Instead of
"A1:A10, C1:C10"
maybe
"A1:A10", "C1:C10"
Though maybe not, too. The example I've given is equivalent to "A1:C10" and may not be what you want.
You may want
with xlwb.sheets(1)
Set r = Union(.Range("A1:A10"),.Range("C1:C10"))
end with
If so, you'll need to manipulate your text to achieve the result.
HTH,
Fazza