When AP 3.0 was released, Apple added a new rendering engine and the local adjustment brushes. Upgrading at that time required that the library be upgraded also to use the new features. Users had the option of upgrading the library database (and internal support files) only, or to opt for updating all images to allow use of the local adjustment features (brushes) on those images.
There have been additional updates that required the library to be updated also (AP 3.1, 3.2, 3.3 and 3.4 if memory serves). There may have been a couple of additional ones, but those 3.x updates added key features.
I suspect you may need to update your current library to AP 2.1.4 > make a copy for backup > upgrade library to AP 3. You may be able to upgrade directly from 2.1.4 to 3.4.1, but I am not sure since I went from 2.1.4 to 3.0.
If you have OS X 10.8.2 on the new machine, I am not sure if AP 2.1.4 can be run (hopefully others can answer that one). Merging and exporting projects as a library were one of the features in AP 3, so you must have a library at that level to do that type of procedure.
Here is a link to the update features and you will see some recommendations at the bottom for upgrading the libraries for use with AP 3. 😉
Sorry, forgot the add the link:
http://support.apple.com/kb/TS2518
Message was edited by: CorkyO2 to add link to release notes
