The dreaded HDR halo. My friend Jim Begley is the master of HDR. Fortunately for His Light Workshops, he'll share that knowledge with you. All to often halo appear around where light bright skies meet dark object in HDR images. It happens to me and I am sure it happens to you. The only real way to get rid of them is to have the original set of images and use a layer mask. I don't have the original images and I'm not going to try to fake it in Photoshop.
The Snake Tips
Thinking Critically about Photographs