I’m a happy user of Adobe Lightroom 4.4 for years, and for years I had an issue when importing catalogues from Mac to PC. For example I imported pictures from a card to my PC, did some editing, exported all the files (including digital negatives) to my MacBook. Did some more editing, selection etc. (e.g. with customer on site), and I always used to get „Lightroom could not import this catalog because of an unknown error“ whilst trying to re-import the catalogue back to my PC. Today I hopefully solved the problem, although more testing might be needed.

1) Export the catalogue on Mac, save the exported catalogue to PC
2) Open the catalogue in Lightroom.
3) Link the missing files to the catalogue (in library left hand side right click on the folder name and select „update folder location“ follow the instructions), the pictures should now have working preview.
4) save the catalogue to PC under new name
5) open you main picture catalogue
6) import the catalogue made in step 4, it should be all working!

I did not tested this solutions in another versions of Lightroom, other than 4.4, and on another platforms, e.g. PC to PC, Mac to Mac or Mac to PC, only Mac to PC.

It would be great if you leave your comments and feedback!