Can't call Excel Services UDF from macro, object not found error

Hello,

I am attempting to call an Excel Services UDF explicitly from a macro
(invoked by a button click).

I registered the Excel Services UDF as a COM add-in as outlined in the
article (http://msdn2.microsoft.com/en-us/library/bb267252.aspx), and can
invoke the UDFs using cell references (i.e. =HelloWorld())

However, when I try to invoke a UDF in a macro, it failed with object not
found. I tried prefixing the namespace, etc, no luck
XlUnlimitedUDFs.HelloWorlds()
XlUnlimitedUDFs.XlUnlimitedUDFs.HelloWorld()

Thanks a million,
Alex