In Magento EE 1.14 and and CE 1.9 are responsive emails introduced.
If you use "{{template config_path="design/email/header"}}" in a email template, it loads an email template that is set in "System > Configuration > General > Design > Transactional Emails".
However, if the email template that is selected in that setting also uses "{{template config_path="design/email/header"}}", then it creates an infinite loop.
That can result in a white page, an error 500 page, a 'maximum nesting level reached' error, an 'execution timeout' error or a 'memory size exhausted' error.
This error is not specific for Cart2Quote, but would affect your whole store, so it is advisable to check if this is not te case.