Parameterised queries

I am having enormous trouble trying to get parameterised queries to work
in a Delphi 1/OBDC/Personal Oracle 7 environment. Non-parameterised
queries are fine, but any parameterised query results in the following
error message :

General SQL error - ORA-01480 - trailing null missing from STR bind
variable.

The parameters are set from within the code using the ParamByName method
and I have checked the values of the parameters before the query is
executed and they contain the values I expect.

I have tried different versions of the BDE, the most recent one being the
one that comes on the Delphi2 CD - I don't know what version that is, and
 even tried 32 bit ODBC drivers, but the result is always the same. I
have viewed the ODBC trace log and this seems OK to me.

I am fed up with this, as I know it should work - and exactly the same
code does work at another installation!

Help!! It will be very much appreciated!