I get the error directly when querying:

http://www.google.de/base/feeds/snippets/-/immobilien?start-index=1&max-results=250&crowdby=customerid:40&bq=[location:+@"+52.536390+13.605859"+10mi][listungstyp:zu%20vermieten][target%20country:DE]&content=all

Removing the [Location:] fixes the problem, but then I can't search by location.

I've followed Google location query example exactly found at: http://code.google.com/apis/base/attrs-queries.html#LocDatQuer

The lat/lng being used is valid, as google maps find the location (near Berlin), using the google base front I know there are items in the area as they show up.

I've also trued URL encoding the " and [ but with no success.

Any suggestion, what does "cannot map type set to a single type" even mean?