File not found localhost website (xampp)

if you're sure the file is where you think it is (and I put that in bold because you have no idea how many times I've helped people who were so sure a file was there that they didn't bother to look), then something's going wrong with the path construction you're doing. have you put in a debugger statement just before the require once? something like var_dump(LIB_PATH.DS.'cljsdb.inc.php'); - that should print out the path it's trying to include so you can check that it's building the string correctly.

If the path is correct and the file is there, it may be a permissions issue. I don't remember if php is smart enough to distinguish between a file it can't find and a file it can't open.

A quick glance at the docs - (Mac) (WIndows) - shows that the installation methods are entirely different. Windows had an installer that puts components into the system, while Mac has a self-enclosed application. Obviously unix and windows have different low-level system directory structures, but I suspect that the application merely redirects the system to use its own internal php.ini file and folder structure. You may be over-engineering: packages like this on the Mac are often designed to be opaque with high-level access points, so that it's easier and quicker to get things up and running. You'll have to check with the XAMMP people to get the details.