Migrating ForeignField to OneToOneField

[Jonathan]

I'm using South to migrate a certain field from ForeignField to
OneToOneField.
Initial state is that I have model A pointing to model B using a
ForeignField. Of course there's only one instance of A pointing to a B
instance.

I wasn't sure if this would work directly, or that I should do a 3-
stage migration (1- add a different field, 2- copy the id from
ForeignField to OneToOneField, 3- erase the ForeignField), so I tried
it and it worked flawlessly on my local machine - Windows\django 1.1.0
final\Python 2.6.4\MySQL 5.1.41

Unfortunately, I ran the migration on our development server which is
a Debian\django 1.1.0 beta\Python 2.5.0\MySQL 5.0.32 and the migration
failed with the following error:

Traceback (most recent call last):
File "/usr/lib/python2.5/site-packages/South-0.6_pre-py2.5.egg/south/
migration.py", line 315, in run_migrations
runfunc(orm)
File "/usr/share/<location and filename>", line 19, in forwards
db.create_unique('tree_family_name', ['base_id'])
File "/usr/lib/python2.5/site-packages/South-0.6_pre-py2.5.egg/south/
db/generic.py", line 346, in create_unique
self.execute("ALTER TABLE %s ADD CONSTRAINT %s UNIQUE (%s)" % (qn
(table_name), qn(name), cols))
File "/usr/lib/python2.5/site-packages/South-0.6_pre-py2.5.egg/south/
db/mysql.py", line 29, in execute
return generic.DatabaseOperations.execute(self, sql, params)
File "/usr/lib/python2.5/site-packages/South-0.6_pre-py2.5.egg/south/
db/generic.py", line 70, in execute
cursor.execute(sql, params)
File "/usr/lib/python2.5/site-packages/django/db/backends/util.py",
line 19, in execute
return self.cursor.execute(sql, params)
File "/usr/lib/python2.5/site-packages/django/db/backends/mysql/
base.py", line 84, in execute
return self.cursor.execute(query, args)
File "/usr/lib/python2.5/site-packages/MySQLdb/cursors.py", line
163, in execute
self.errorhandler(self, exc, value)
File "/usr/lib/python2.5/site-packages/MySQLdb/connections.py", line
35, in defaulterrorhandler
raise errorclass, errorvalue
OperationalError: (1061, "Duplicate key name
'tree_family_name_base_id'")

Is this due to the django version? Python version? MySQL version? Any
thoughts? Should I change to the 3-stage migration model?

[Jonathan]

Solved.
It wasn't the OS, django, Python or MySQL versions...
It was the South version. Locally I was using 0.6.2 whereas the on the
development server I had 0.6-pre installed.
btw, if you encounter this and try to "python setup.py install" the
new South - remember to erase the old South folders and egg files from
the site-packages directory... Interestingly enough if you don't do
that in Python's shell you'll get the new South version, whereas in
django's shell you'll get the old south version.....
Jonathan