Warning: I'm a bit of a newbie in Oracle, so please give a 10 second head start before you get out your flame thrower ;-))
I'm not the administrator of the DB I'm dealing with, just a volunteer trying to help a NGO with their website

I have a problem with a SELECT in Oracle:
I want to select records with text that contans a certain searchstring.
The following query just returns an errormessage:
SELECT header, id FROM section WHERE text like '%Afghanistan%'

Errormessage: ORA-00932: inconsistent datatypes

So I tried
SELECT header FROM section WHERE dbms_lob.INSTR(text, 'Afghanistan')>0
But this query always returns only 1 record.

Apparently the text is not stored as text, but as some form of lob.

How can I reliably select ALL records, that contain given string?

If the LOB is of the type CLOB, this should return you all the rows.
Try the same using yasql (available on the net) and run the command back again.