Django BD error

Hi guys i´m using Django 1.7 and mysql to create an application and I´m receiving this error

ValueError at /Cannot create form field for 'radiotipo_idradiotipo' yet, because its related model u'Radioinfo' has not been loaded yet

I don´t know what is this. this error happenes on my forms.py, here´s the code: forms.py

from django import forms
from models import Node, Datasource, Radio, Radiotipo, Snapshot, Tag, Taginfo, Valores

class NodeForm(forms.ModelForm):
    class Meta:
        model = Node

class DatasourceForm(forms.ModelForm):
    class Meta:
        model = Datasource
class RadiotipoForm(forms.ModelForm):
    class Meta:
        model = Radiotipo
class SnapshotForm(forms.ModelForm):
    class Meta:
        model = Snapshot
class TagForm(forms.ModelForm):
    class Meta:
        model = Tag
class TaginfoForm(forms.ModelForm):
    class Meta:
        model = Taginfo
class ValoresForm(forms.ModelForm):
    class Meta:
        model = Valores
class RadioForm(forms.ModelForm):
    class Meta:
        model = Radio

and here is my models.py

class Datasource(models.Model):

    objects = GChartsManager()

    idestacao_meteo = models.IntegerField(db_column='idDATASOURCE', primary_key=True, editable=False)  # Field name made lowercase.
    nome_estacao = models.CharField(db_column='NAME', max_length=45)  # Field name made lowercase.
    fabricante = models.CharField(db_column='MANUFACTURER', max_length=45, blank=True)  # Field name made lowercase.
    modelo = models.CharField(db_column='MODEL', max_length=45, blank=True)  # Field name made lowercase.
    node_idnode = models.ForeignKey('Node', db_column='site_idSITE', blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'datasource'


class Node(models.Model):

    objects = GChartsManager()

    idnode = models.IntegerField(db_column='idSITE', primary_key=True, editable=False)  # Field name made lowercase.
    nome = models.CharField(db_column='NAME', max_length=45)  # Field name made lowercase.
    informacoes = models.CharField(db_column='DESCRIPTION', max_length=45, blank=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'site'

class Radio(models.Model):

    objects = GChartsManager()

    idradio = models.IntegerField(db_column='idRADIO', primary_key=True, editable=False)
    endreal = models.CharField(db_column='ENDREAL', max_length=64, blank=True)  # Field name made lowercase.
    radiotipo_idradiotipo = models.ForeignKey('Radioinfo', db_column='radioInfo_idRADIOINFO')  # Field name made lowercase.
    datasource_idestacao_meteo = models.ForeignKey(Datasource, db_column='datasource_idDATASOURCE', blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'radio'

class Radiotipo(models.Model):

    objects = GChartsManager()

    idradiotipo = models.IntegerField(db_column='idRADIOINFO', primary_key=True, editable=False)  # Field name made lowercase.
    nome = models.CharField(db_column='NAME', max_length=45)
    descricao = models.CharField(db_column='DESCRIPTION', max_length=300, blank=True)

    class Meta:
        managed = False
        db_table = 'radioinfo'

class Snapshot(models.Model):

    objects = GChartsManager()

    idsnap = models.IntegerField(db_column='idSNAP', primary_key=True, editable=False)  # Field name made lowercase.
    valor = models.FloatField(db_column='VALUE', blank=True, null=True)  # Field name made lowercase.
    snapshot = models.DateTimeField(db_column='SNAPSHOT', blank=True, null=True)  # Field name made lowercase.
    tag_idtag = models.ForeignKey('Tag', db_column='tag_idTAG')  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'snapshot'

class Tag(models.Model):

    objects = GChartsManager()

    idtag = models.IntegerField(db_column='idTAG', primary_key=True, editable=False)  # Field name made lowercase.
    desvio = models.FloatField(db_column='DEVIATION', blank=True, null=True)  # Field name made lowercase.
    tempo_max = models.IntegerField(db_column='TIME_MAX', blank=True, null=True)  # Field name made lowercase.
    conv_rate = models.IntegerField(db_column='CONV_RATE', blank=True, null=True)  # Field name made lowercase.
    taginfo_idtaginfo1 = models.ForeignKey('Taginfo', db_column='tagInfo_idTAGINFO')  # Field name made lowercase.
    datasource_idestacao_meteo = models.ForeignKey(Datasource, db_column='datasource_idDATASOURCE', blank=True, null=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'tag'

class Taginfo(models.Model):

    objects = GChartsManager()

    idtaginfo = models.IntegerField(db_column='idTAGINFO', primary_key=True, editable=False)  # Field name made lowercase.
    nome = models.CharField(db_column='NAME', max_length=45)  # Field name made lowercase.
    descricao = models.CharField(db_column='DESCRIPTION', max_length=255, blank=True)  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'taginfo'

class Valores(models.Model):

    objects = GChartsManager()

    idvalores = models.IntegerField(db_column='idVALUES', primary_key=True, editable=False)  # Field name made lowercase.
    valor = models.FloatField(db_column='VALUE')  # Field name made lowercase.
    datahora = models.DateTimeField(db_column='DATETIME')  # Field name made lowercase.
    tag_idtag = models.ForeignKey(Tag, db_column='tag_idTAG')  # Field name made lowercase.

    class Meta:
        managed = False
        db_table = 'values'

Thanks for helping.