PHP-ext-couchbase 1.1.0-dp5 - failed to create IO Instance - CentOS 5.4

I'm am having a problem running php-ext-couchbase 1.1.0-dp5...

Specifications

- CentOS release 5.4 (Final)
- PHP 5.3.18

Here is what I did to install 1.1 on CentOS 5.4...

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# You need to install libev
wget http://dl.fedoraproject.org/pub/epel/5/x86_64/libev-4.03-2.el5.x86_64.rpm
rpm -Uvh libev-4.03-2.el5.x86_64.rpm

# You need to install the preview couchbase repo
wget -O/etc/yum.repos.d/couchbase.repo http://packages.couchbase.com/preview/rpm/couchbase-centos55-x86_64.repo
yum check-update

# You need to install lib couchbase
yum -y install libcouchbase-devel

# You need to get the latest 1.1.0-dp5 code
wget http://packages.couchbase.com/clients/php/php-ext-couchbase-1.1.0-dp5-ce...

# Untar and copy over the couchbase.so
tar -zxvmpf php-ext-couchbase-1.1.0-dp5-centos55-x86_64.tar.gz
cp php-ext-couchbase/couchbase.so /usr/lib64/php/modules/couchbase.so

# Append extension=couchbase.so to end of /etc/php.d/json.ini
echo extension=couchbase.so >> /etc/php.d/json.ini
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Within membasetest.php I used the example code... xxxxxxxxxx is our couchbase 1.8.1 cluster host name

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<?php
// adjust these parameters to match your installation
// this example is for the default bucket, the third argument is the password
$cb = new Couchbase("xxxxxxxxxx:8091", "default", "", "default" );
$cb->set("a", 1);
var_dump($cb->get("a"));
?>
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When I run php -f membasetest.php
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PHP Warning: Couchbase::__construct(): failed to create IO instance in membasetest.php on line 4
PHP Warning: Couchbase::set(): unintilized couchbase in membasetest.php on line 5
PHP Warning: Couchbase::get(): unintilized couchbase in membasetest.php on line 6
bool(false)
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Can anyone please help me out with this problem?

Ben