Limit on lenght in columns

[Matteo Gattoni]

Hello,
I have a column varchar(4000) in a table.
When I use it, I have some problems:
1) 
    SELECT s.*
    FROM SEGMENT_TYPE s
    order by s.c_tree_path

    give me the error    
General error;-1013 POS(2001) Too many order columns.

We resolve the problem using 
    Select s.*
    from segment_type s
    order by substr(s.c_tree_path, 1, 1000).

    That exclude from the query the other 3000 caracters of the field.

2) Concatenating strings I found the error : too long row, when the row obtained is 
longer than 1000.

Is there a parameter thata fix the limit to 1000?
Is something with my first query that make me able to use all the 4000 caracters in 
the field?

Thanks,

Matteo