I use a PC as a "master" desktop and a Mac as a "travel" laptop. Both have latest version LR 2015.6.1. I attempted to import a travel catalog into the PC Master and kept getting "LR could not import this catalog because of an unknown error". Previously I copied the entire catalog folder into my Master image folder. During the prompts LR recognized the correct travel catalog and the images in seven different sub-folders. Got error message when I selected all folders, and also when I just selected only one image sub-folder.
Previously I looked at Julieanne's always excellent tutorials on the subject, however her 2015 tutorial showed different prompts. Irritating for sure.
Advice would be much appreciated; would hate to lose all that developing time and effort I expended on the road.
I believe I have solved my own problem. Both the Mac and the PC catalogs worked fine on their respective machines, I manually copied the Mac folder that contained the images and the .lrcat and .lrdata files over to where I wanted them to reside on my Master PC (actually a connected external drive). I then opened the copied Mac catalog on the PC and it loaded up and worked fine. I noticed during this operation I may have had two sub-folders named the same as ones in my Master PC files, so I renamed them using LR. Closed this catalog and reopened the Master catalog, and then did an "import using another catalog" and it completed successfully as advertised.
Not sure what did the trick, either the renaming of a couple of duplicate sub-folder names or the catalog integrity / compatibility check with the manual copy and run on the Master PC, but hey, it worked. Invested quite a few hours on that one!