problem adding foreign key...

[Albert Mata]

In TABLE1 there is a field called VLO_COD_ACC (varchar(6)).

In TABLE2 the first two fields are...
ste_int varchar(6)
ste_id smallint(5) unsigned auto_increment
...both are not null and primary key.

I'm trying to add a foreign key this way:

alter table TABLE1 add foreign key(VLO_COD_ACC) references TABLE2(ste_int);

But I get an error and when I take a look at SHOW ENGINE INNODB STATUS; I can see this:

Cannot find an index in the referenced table where the
referenced columns appear as the first columns, or column types
in the table and the referenced table do not match for constraint.

Which in my opinion isn't true at all as there is an index in the referenced table where the referenced column (ste_int) appear as the first column and column types are both times varchar(6).

Does anyone know what's wrong with it?

Many thanks in advance.