iFrame stopped working

Hi… I had iFrame working nicely displaying a google map. Now it has suddenly stopped working – I just get a blank space where the map should be.

My short code is:
[iframe src=”https://maps.google.com/maps?q=http:%2F%2Fblog.antipole.co.uk%2Ffiles%2F2013%2F05%2FStart-to-Maryport.kml&hl=en&ll=52.5,-4.20&spn=4.3,9.07&t=h&output=embed”%5D

The src string (The string in “”) works fine when invoked as a link. Test site with all other plug-ins deactivated here.
Wonder if WP 3.8.1 has broken it. Has anyone else had this problem?

https://ww.wp.xz.cn/plugins/iframe/