Invoice receipt not sending?

I have enabled both E-Mail Payment Receipt to user and Admin Payment Notifications enabled Inside the Setup -> Email page but my users are not receiving the invoice via email, im not using the PDF invoice, that is disabled, they are receiving other e-mails such as a approval email e.c.t
I have been looking at this for a few hours now and very confused why it isn't working, any ideas?

Can you paste a screenshot of your email settings?

David

These are my email settings,

http://postimg.org/image/6s206ebrr/

E-mails send fine, I have the invoice option set but they don't send out. They aren't any errors in the system logs either, very confused :s

Don't you have to enable PDF emails? Cannot remember.

No i have that option disabled, playing around with it, turning it On/Off doesnt make a difference.

The copy of invoice to admin email isn't sending either :s

Sorry for double posting,

I am using the WorldPay plugin, would this affect it?

Actually when I do go to Setup -> PDF Invoice I get the following error:

Code:

Fatal error: Declaration of Zend_Pdf_FileParserDataSource_String::__construct() must be compatible with Zend_Pdf_FileParserDataSource::__construct() in C:\inetpub\wwwroot\site1\applications\library\Zend\Pdf_Pack.php on line 192 

Would submit ticket to aMember then.