It's possible that some versions of ZODB give a problem with python 2.5 if you don't create an empty database manually the first time you execute Indico.

Create an empty database by executing the following script:

import ZODB
from ZODB import FileStorage, DB
import transaction

storage = FileStorage.FileStorage("data.fs")
db = DB(storage)
connection = db.open()
dbroot = connection.root()

transaction.commit()

connection.close()
db.close()
storage.close()