After some testing it looks like a permissions issue on the _promaps_cache directory. Trying giving that directory (and the file inside to be safe) write permissions. Make sure its not set to read only too.
Here is what the XML looks like:
<geocode_data version="1.0">
<geocode_entry ID="George Street Sydney New South Wales 2000 Australia">
<address>
George Street, Sydney, New South Wales, 2000, Australia
</address>
<geocode>(-33.868737, 151.206946)</geocode>
</geocode_entry>
</geocode_data>