Rollover code not working in wordpress 3.9.1

I have been using this simple code to generate image roll overs for images however it not longer seems to work. Does any one know why and what I can do to get it working again.

<img src=” URL_IMG-1 ” onmouseover=”this.src=’ URL_IMG-2 ‘” onmouseout=”this.src=’ URL_IMG-1 ‘” />

Failing that can anyone recommend a simple plugin please.

Many thanks