Nominatim internal server error

I'm running Nominatim on my server and I recently (2 weeks ago) imported full planet data. I'm assuming the import is complete (not sure if it is, as the output never explicitly stated "finished"). Here's my import output:

Done 87399141 in 624893 @ 139.862564 per second - Rank 30 ETA (seconds): -30.558571
Done 87399213 in 624894 @ 139.862473 per second - ETA (seconds): -31.073381
Done 87399213 in 624894 @ 139.862473 per second - FINISHED
...
CREATE INDEX
CREATE INDEX
CREATE INDEX

Postgres doesn't appear to be doing anything either:

[root~]# psql postgres
psql (9.1.9)
Type "help" for help.

postgres=# select * from pg_stat_activity;
 datid | datname  | procpid | usesysid | usename | application_name | client_addr | client_hostname | client
_port |         backend_start         |          xact_start           |          query_start          | wait
ing |          current_query
-------+----------+---------+----------+---------+------------------+-------------+-----------------+-------
------+-------------------------------+-------------------------------+-------------------------------+-----
----+---------------------------------
 12780 | postgres |   31281 |    16385 | root    | psql             |             |                 |
   -1 | 2014-02-26 11:52:00.615982-08 | 2014-02-26 11:52:10.074218-08 | 2014-02-26 11:52:10.074218-08 | f
    | select * from pg_stat_activity;
(1 row)

Having said that, I'm trying to reverse geocode via Nominatim, but it's giving me error messages:

Query:

http://my-servers-ip-address/nominatim/reverse?format=xml&lat=40.731389&lon=-73.998889&zoom=18&addressdetails=1

Output:

Internal Server Error
Nominatim has encountered an internal error while processing your request. This is most likely because of a bug in the software.
Details: Could not determine closest place. Feel free to report the bug in the http://trac.openstreetmap.org OSM bug database. Please include the error message above and the URL you used.

How can I debug to see what went wrong? Could the import have gone wrong? (Nominatim, the same installation on the same machine, was working fine before I wiped the database and imported new data) Is the import actually not finished?

Thanks

EDIT:

Adding apache error message and debug=1 option in the URL:

Apache error message:

[Fri Feb 28 09:56:49 2014] [error] an unknown filter was not added: proxy-html
[Fri Feb 28 09:56:49 2014] [error] [client my-ip-address] PHP Fatal error:  Cannot use object of type DB_Error as array in /postgres/OpenStreetMaps/Nominatim-2.2.0/lib/PlaceLookup.php on line 53

Output with debug=1 option:

string(561) "select place_id,parent_place_id,rank_search from placex WHERE ST_DWithin(ST_SetSRID(ST_Point(-73.998889,40.731389),4326), geometry, 0.0008) and rank_search != 28 and rank_search >= 30 and (name is not null or housenumber is not null) and class not in ('waterway','railway','tunnel','bridge') and indexed_status = 0  and (ST_GeometryType(geometry) not in ('ST_Polygon','ST_MultiPolygon')  OR ST_DWithin(ST_SetSRID(ST_Point(-73.998889,40.731389),4326), centroid, 0.0008)) ORDER BY ST_distance(ST_SetSRID(ST_Point(-73.998889,40.731389),4326), geometry) ASC limit 1"