This is my captcha setting
'captcha'=>array(
'class'=>'CCaptchaAction',
'backColor'=>0xFFFFFF,
'foreColor'=>0xFF712E,
'offset'=>-3,
'height'=>45,
'testLimit'=>1,
),
In this case Captcha entered always is invalid, but when testLimit set to more than 1, it work’s correctly. what’s the problem 
Ajax and Client Validation is disabled.
EDIT: Captcha works on Contact form without any problem !!!
register.php (form)
<div class="form wide">
<?php $form=$this->beginWidget('CActiveForm', array(
'id'=>'register-form',
)); ?>
<div class="row">
<?php echo $form->label($model,'username'); ?>
<?php echo $form->textField($model,'username'); ?>
<?php echo $form->error($model,'username'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'email'); ?>
<?php echo $form->textField($model,'email'); ?>
<?php echo $form->error($model,'email'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'password'); ?>
<?php echo $form->passwordField($model,'password'); ?>
<?php echo $form->error($model,'password'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'password_confirm'); ?>
<?php echo $form->passwordField($model,'password_confirm'); ?>
<?php echo $form->error($model,'password_confirm'); ?>
</div>
<?php if(CCaptcha::checkRequirements()): ?>
<div class="row">
<?php echo $form->label($model,'verifyCode'); ?>
<?php echo $form->textField($model,'verifyCode'); ?>
<?php echo $form->error($model,'verifyCode'); ?>
<div class="captcha">
<?php $this->widget('CCaptcha',array(
'buttonLabel'=>Yii::t('form','Get new code'),
//'clickableImage'=>true,
'imageOptions'=>array('class'=>'image'),
'buttonOptions'=>array('class'=>'button'),
)); ?>
</div>
</div>
<?php endif; ?>
<div class="row buttons">
<?php echo CHtml::submitButton(Yii::t('form','Submit')); ?>
</div>
<?php $this->endWidget(); ?>
</div><!-- form -->
[b]Contact.php /b:
<?php if(Yii::app()->user->hasFlash('contact')): ?>
<div class="flash-success">
<?php echo Yii::app()->user->getFlash('contact'); ?>
</div>
<?php else: ?>
<div class="form wide">
<?php $form=$this->beginWidget('CActiveForm', array(
'id'=>'contact-form',
)); ?>
<div class="row">
<?php echo $form->label($model,'name'); ?>
<?php echo $form->textField($model,'name'); ?>
<?php echo $form->error($model,'name'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'email'); ?>
<?php echo $form->textField($model,'email'); ?>
<?php echo $form->error($model,'email'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'subject'); ?>
<?php echo $form->textField($model,'subject',array('size'=>60,'maxlength'=>128)); ?>
<?php echo $form->error($model,'subject'); ?>
</div>
<div class="row">
<?php echo $form->label($model,'body'); ?>
<?php echo $form->textArea($model,'body',array('rows'=>6, 'cols'=>50)); ?>
<?php echo $form->error($model,'body'); ?>
</div>
<?php if(CCaptcha::checkRequirements()): ?>
<div class="row">
<?php echo $form->label($model,'verifyCode'); ?>
<?php echo $form->textField($model,'verifyCode'); ?>
<?php echo $form->error($model,'verifyCode'); ?>
<div class="captcha">
<?php $this->widget('CCaptcha',array(
'buttonLabel'=>Yii::t('form','Get new code'),
//'clickableImage'=>true,
'imageOptions'=>array('class'=>'image'),
'buttonOptions'=>array('class'=>'button'),
)); ?>
</div>
</div>
<?php endif; ?>
<div class="row buttons">
<?php echo CHtml::submitButton('Submit'); ?>
</div>
<?php $this->endWidget(); ?>
</div><!-- form -->
<?php endif; ?>
Controller/actionSignup:
public function actionSignup()
{
$model = new NewUser('register');
if(isset($_POST['NewUser']))
{
$model->attributes = $_POST['NewUser'];
if($model->validate())
if($model->save()){
$url = Yii::app()->createAbsoluteUrl('site/verify',array(
'type'=>'user', 'verifyString'=>$model->verify_string));
send_verify_code($url,null,$model->email);
$this->render('notify',array('status'=>'registered'));
Yii::app()->end();
}
}
$this->render('register',array('model'=>$model));
}
Controller/actionContact:
public function actionContact()
{
$model=new ContactForm;
if(isset($_POST['ContactForm']))
{
$model->attributes=$_POST['ContactForm'];
if($model->validate())
{
$name='=?UTF-8?B?'.base64_encode($model->name).'?=';
$subject='=?UTF-8?B?'.base64_encode($model->subject).'?=';
$headers="From: $name <{$model->email}>\r\n".
"Reply-To: {$model->email}\r\n".
"MIME-Version: 1.0\r\n".
"Content-type: text/plain; charset=UTF-8";
mail(Yii::app()->params['adminEmail'],$subject,$model->body,$headers);
Yii::app()->user->setFlash('contact','Thank you for contacting us. We will respond to you as soon as possible.');
$this->refresh();
}
}
$this->render('contact',array('model'=>$model));
}
NewUser Model->rules:
public function rules()
{
// NOTE: you should only define rules for those attributes that
// will receive user inputs.
return array(
array('username, email, password', 'required'),
array('username', 'length', 'min'=>3,'max'=>50),
array('username', 'verifyUser'),
array('email', 'length', 'max'=>255),
array('email', 'email'),
array('email', 'verifyEmail'),
array('password', 'length', 'min'=>4, 'max'=>60, 'allowEmpty'=>false),
array('password', 'compare', 'compareAttribute'=>'password_confirm', 'on'=>'register'),
array('password_confirm','safe', 'on'=>'register'),
// verifyCode needs to be entered correctly
array('verifyCode', 'captcha', 'allowEmpty'=>!CCaptcha::checkRequirements()),
// The following rule is used by search().
// Please remove those attributes that should not be searched.
array('id, username, email, password, verify_string', 'safe', 'on'=>'search'),
);
}
Contact Model->rules:
public function rules()
{
return array(
// name, email, subject and body are required
array('name, email, subject, body', 'required'),
// email has to be a valid email address
array('email', 'email'),
// verifyCode needs to be entered correctly
array('verifyCode', 'captcha', 'allowEmpty'=>!CCaptcha::checkRequirements()),
);
}