When upgrading to a new LR version you NEVER reimport.
You convert your latest catalog from the old version by opening it in the new version.
Thus you will have all folder structures automatically available, plus keywords, collections, develop history.
Throw away any potentially created new catalog of the new version.
BTW rather install the latest download of LR4.1RC than a boxed version of 4.0 due to bug fixes.
Thanks for your response. I am not, however, moving from Ver 2.7 to 4.0. I am simply trying to copy everything from one PC to another using the same Ver 2.7.
When I click File > Open Catalog, I was hoping to click on my Master_Catalog and there would be light, so to speak. Doesn't happen. Could it be that the catalog I want to open - or that LR is looking for - is in a location other than my folder called C:/Lightroom_catalogs?
The catalog location can be found by launching LR on the old computer and selecting Edit->Catalog Preferences. It will be a file with extension .LRCAT (might be lower case) Make sure you have moved this *.LRCAT file to the new computer, and then open Lightroom and File->Open Catalog and point it to the .LRCAT file.