Hello,
the following commands raise an error "ORA-01008: not all variables bound":

create table t (col1 number(1), col2 varchar2(3), col3 number(1));
define v=1
insert into t values(&v, '--', &v);
commit;
drop table t;

The PL/SQL Developer command processor seems to have a problem with the string '--'.
This problem does not occur in SQL*Plus.

I run the current Version 7.1.5.1398

Regards
Frank

We'll fix it. A possible workaround is:

insert into t values(&v, '-'||'-', &v);