Cannot create credit memo for orders placed by Guests (NON LOGGED IN customer group)

Question

I am using Magento CE 1.7.0.2. Now the problem I face is that, if I attempt to create a credit memo for an order which is placed by a guest (ie. NON LOGGED IN customer group), it shows an error as follows:

"Customer email is required."

Although I can create an Invoice without any issue. The payment methods are:

1. Check /Money Order
2. Express NAB Transact (Authorize and Capture mode)
3. Paypal Checkout

The only extension I am using that affects the checkout procedure is "Customer Credit Extension" from Magestore.

So is it because of that extension I am using or some other magento problem??

Any help will be appreciated!!

Answer 1

In order to check if the extension is the problem, just disable it, create an order, invoice it, and try to create a credit memo.

_{Because @benmarks requested, I've written this as an answer.
He made me do it. I didn't want to. :)}