Can you upgrade to LR 5.6 or re-install LR 5.6 and see if the problem goes away? Are you using the Cloud version of LR or the standalone-serial-number version?
"An error occurred attempting to change modules". Any ideas how to fix/get around??
Look to the right of this page, under "MORE LIKE THIS".
I had the same issue trying to install on an I Mac.I solved the problem by just creating another user for my computer and when I installed under the new user it worked. This after several days of total frustration. Hope this works for you, Ken K
See my answer to Marina44. It worked for me.Ken K