I recently upgrade to Lightroom 5.7.1 and have noticed that when I am trying to create an HDR image using the "Photo->Edit In->Merge to HDR Pro in Photoshop" no longer works. Photoshop will launch but the images do not appear and no HDR merge processing is done. I'm using Photoshop CS5 Version 12.0. My OS is Mac OSX Version 10.9.5.
The Merge to HDR has worked consistently in the past and I'm experiencing the same issue on both my iMac and Airbook machines (running identical software - OS, PS, LR).