Ambiguous expressions - Help!

[Mike H <postmaster@ada-augusta.demon.co.uk>]

package Foo1 is
   type grid_index_type  is new integer range 0..80;
   type grid_type is array (grid_index_type range <>) of character;
   subtype Vector_type is grid_type (0 .. 8);
... etc.

with Foo1;
package Foo2 is
   procedure Put_line (Item : in Foo1.Vector_type);
   procedure Put_line (Item : in string);
... etc.

with Foo1; use Foo1;
with Foo2;
procedure Foo3 is
   Foo_thing : Vector_type;
begin
... etc.
   Foo2.Put_line (Foo_thing);
... etc.
   Foo2.Put_line ("Something else");
... etc.
end Foo3;

Compilation of Foo3 raises error messages of the form "ambiguous
expression (cannot resolve "Put_line")

I find it hard to believe that the compiler cannot distinguish between a
string and an array of characters. What am I doing wrong?
-- 
Mike
Swim? Naturally at Severn Vale
<http://www.severnvalesc.org/>