New Email Template save failing "404 error: Page not found."

[cci1]

After I create a new email template and hit 'Save Template' it returns with a 404 page not found error. Checking the templates list after that shows it didn't save. "Preview Template" also results in the same.

Anyone know how to fix this?

Magento 2.1.7  

Thanks

[cci1 · Accepted solution]

Solved this if anyone is interested. Our Hosts mod_security was getting tripped by this, they added an exception and it works fine now..