Error adding tracking pixel to an email

Hi everyone,

I'm trying to add a tracking pixel to an email but when I want to send a test or approve the email I'm getting an error: Parse Template call failed (with the whole email code).

All I'm adding is the image for the pixel (I haven't touched anything else) and I've tried adding it in the HTML & by using the insert image button in the editor.

Is this a system error or is it something I'm doing?

Any help is much appreciated!

Thanks.