SQL & PL/SQL

I'm trying to learn Oracle Spatial working with 11g R2 and with 3D georeferenced data (specifically data describing buildings in a city).

But I'm having trouble getting a basic query to work on my dataset (it works for the book example), and I'm trying to do it exactly the way it's done in the Spatial Developer's Guide for 11g.

To learn how spatial queries work, I set up the cola_markets tables used in the book, made the appropriate manual entry in the user_sdo_geom_metadata view and created the index. Having done that, I can run the following simple query (as well as the others in the manual) on the book tables:

SELECT SDO_GEOM.SDO_DISTANCE(c_b.shape, c_d.shape, 0.005)
FROM cola_markets c_b, cola_markets c_d
WHERE c_b.name = 'cola_b' AND c_d.name = 'cola_d';

but when I try to do the same thing on my own tables (created from citygml data), I get an error. There is the difference that the data is 3D, and the index was created without any PARAMETERS ( ... ), hence is just 2D. But still I don't get why the following query doesn't work:

SELECT SDO_GEOM.SDO_DISTANCE(c_w.envelope, c_b.envelope, 0.0005)
FROM cityobject c_w,
cityobject c_b
WHERE c_w.id = 50025
AND c_b.id = 50018;

The id's for the buildings are valid, and I used the same tolerance used by the software that set up the database.

Here's the error I get in SQL developer:

ORA-29532: Java call terminated by uncaught Java exception: java.lang.Exception: 54535
ORA-06512: at "MDSYS.SDO_3GL", line 637
ORA-06512: at "MDSYS.SDO_GEOM", line 1973
ORA-06512: at "MDSYS.SDO_GEOM", line 1990
29532. 00000 - "Java call terminated by uncaught Java exception: %s"
*Cause: A Java exception or error was signaled and could not be
resolved by the Java code.
*Action: Modify Java code, if this behavior is not intended.

So, thinking it might have something to do with the fact that it's a Java interface, I also tried running it from SQL/PL command line and get essentially the same thing:

ERROR at line 1:
ORA-29532: Java call terminated by uncaught Java exception:
java.lang.Exception: 54535
ORA-06512: at "MDSYS.SDO_3GL", line 637
ORA-06512: at "MDSYS.SDO_GEOM", line 1973
ORA-06512: at "MDSYS.SDO_GEOM", line 1990

Any ideas why this isn't working?

(P.S.: I couldn't find a specific board for Oracle Spatial, hence put this question here--if there's a better place for this question, then, admins, of course, feel free to move the thread to the appropriate spot)