"Server Error" when users try to create a new account - Magento 1.7 - magento

Question

I'm setting up our Magento 1.7 store, hoping to be ready for launch soon. I've noticed a problem:
When users try to create a new account, they fill out their info on /customer/account/create page just fine, then when they click submit, they get this 500 Error:
The website encountered an error while retrieving
http://example.com/customer/account/createpost/.
the account is actually created, however.
Similar deal on when users submit their email on the Forgot Password page, they press submit and get this:
The website encountered an error while retrieving
http://example.com/customer/account/forgotpasswordpost/.
no email is sent.
If you see this and know how to help with this prob, your advice would be much appreciated, truly.
In case it helps, we are using a theme, rather than default.
EDIT - (I was asked if I had checked server error)
My server errors show as this, for the above situations:
Forgot Password submit shows this error:
Fatal error: Call to undefined method Mandrill_API::addTo() in
D:\Magento\app\code\core\Mage\Core\Model\Email\Template.php on line
438
and
Create Account submit shows this error:
Fatal error: Call to undefined method Mandrill_API::addTo() in
D:\Magento\app\code\core\Mage\Core\Model\Email\Template.php on line
438
as well.
Here is 6 lines(437-442) of that Template.php file:
foreach ($emails as $key => $email) {
$mail->addTo($email, '=?utf-8?B?' . base64_encode($names[$key]) . '?=');
}
$this->setUseAbsoluteLinks(true);
$text = $this->getProcessedTemplate($variables, true);
[UPDATE]
I've learned that when I enter a random, fake email for Forgot Password, and press submit, a confirmation appears, saying something like "If this email exists, then a new email was sent to that email!", but when I submit an email of a real existing customer, then it gives me the 500 error I've mentioned.
Still nothing - if anyone out there sees this, and you have a bit of time to help solve this perhaps, may Talos bless you!
[SOLVED]
I turns out this was a problem with transaction emails.
Cause by an extension, Mandrill, which is added to magento when I installed the MailChimp extension, called "MageMonkey - MailChimp Integration by ebizmarts"
Once I enabled Mandrill, in config, advanced, all transactions and transaction emails work perfectly fine!

Answer 1

It's possible that it's a .htaccess or server configuration problem. Where is it hosted? Do you have a .htaccess file in the root of the installation?