Hello Mark - I used CS5. I've always used Photoshop for panoramic stitches.
In Lightroom I don't use the edit in > merge to panoramic function, as its never really worked for me. I use edit in > open as layers. Then in Photoshop I select, Edit > Auto-Align Layers > (the program knows it's a panorama) and offers a dialogue box, then I choose - Auto. Sit back and wait while Photoshop does it stuff - the image will need to be blended, so, choose Edit > Blend-layers and hopefully it stitches ok.
If it doesn't, you can click on the relevant layer masks and paint with a soft black or white brush. I save the file as a psd if I'm keeping the editing layers intact, as the overall file size is smaller.
This image is huge, 52mp @ 115cm x 50cm