Thanks for that twenty_one. I didn't have a .lock file, but I did have a 'journal' file which I have now deleted. I am now left with the following:
Lightroom 4 Catalog Previews.lrdata
and
Lightroom 4 Catalog
The only problem is, the second one is not my complete catalog. It only contains the first set of photos I imported when I was trying out the trial version. Is there any way that I can recover my other catalog, and if so, how???
