The error “Deceptive Site Ahead” comes on the browser when Google marks the site as phishing. If you are seeing this error then go to Admin > Site > Settings > SEO/HTML Tab and check if you have added any code or script from an unauthenticated sources that are unsafe to load. If you find any such code or script then remove it and the error will not show.
If you have not added any code or script in the SEO/HTML tab or if the error still exists after removing the code/script, then you may need to contact Google and inform them that they have marked the site incorrectly. You will get an option of informing Google about the site being marked incorrectly on the Error Page. Click on Details and click “Report a Detection Problem” and let Google know that they have marked this site incorrectly.