Python and Sqlite, I am receiving operational error

I will bring below a function code snippet which I can't make to work correct way.

def upload_csv():
    conn = sqlite3.connect("data.db")
    cursor = conn.cursor()

    #as far as tkFileDialog returns absolute path to file, we have to slice from last slash till the end
    filename = fn[fn.rfind("/")+1:]

    cursor.execute("CREATE TABLE IF NOT EXISTS {0}('MSISDN' INTEGER PRIMARY KEY, 'IMEI' TEXT, 'TAC' INTEGER );".format(filename))

    reader = csv.reader(open(fn,'r'))
    for row in reader:
        to_db = [unicode(row[0]),unicode(row[1]),unicode(int(row[2][0:8]))]
        print to_db
        cursor.execute("INSERT INTO data.{0} (MSISDN,IMEI,TAC) VALUES (?,?,?);".__format__(filename), to_db)
        conn.commit()

I receive an Operational error: OperationalError: unknown database May2015