Unable to resolve TabErrors

from flask import (Flask, g, render_template, flash, redirect, url_for)
from flask.ext.bcrypt import check_password_hash
from flask.ext.login import (LoginManager, login_user, logout_user,
                             login_required, current_user)

import forms
import models

DEBUG = True
PORT = 8000
HOST = '0.0.0.0'

from flask_wtf import Form
from wtforms import StringField, PasswordField, TextAreaField
from wtforms.validators import (DataRequired, Regexp, ValidationError, Email,
                               Length, EqualTo)

from models import User


def name_exists(form, field):
    if User.select().where(User.username == field.data).exists():
        raise ValidationError('User with that name already exists.')

import datetime

from flask.ext.bcrypt import generate_password_hash
from flask.ext.login import UserMixin
from peewee import *

DATABASE = SqliteDatabase('social.db')

class User(UserMixin, Model):
    username = CharField(unique=True)
    email = CharField(unique=True)
    password = CharField(max_length=100)
    joined_at = DateTimeField(default=datetime.datetime.now)
    is_admin = BooleanField(default=False)

    class Meta:
        database = DATABASE
        order_by = ('-joined_at',)

        def get_posts(self):
            return Post.select().where(Post.user == self)

    def get_stream(self):
        return Post.select().where(
        (Post.user == self)
        )

    @classmethod
    def create_user(cls, username, email, password, admin=False):
        try:
            cls.create(
                username=username,
                email=email,
                password=generate_password_hash(password),
                is_admin=admin)
        except IntegrityError:
            raise ValueError("User already exists")


class Post(model):
    timestamp = DateTimeField(default=datetime.datetime.now)
    user = ForeignKeyField(
        rel_model=User
        related_name='posts'
    )
    content = TextField()

    class Meta:
        database=DATABASE
        order_by=('-timestamp', )


def initialize():
    DATABASE.connect()
    DATABASE.create_tables([User], safe=True)
    DATABASE.close()