The “Manage Locations” problem appeared to be a Internet Explorer / XP issue. Everything is working Ok on my Windows 7 laptop.
As information, the original problem (Fatal error: Cannot redeclare class SLPPro…) was a real problem. I could not add Pro Pack with Store Locator Plus on release 3.9.5. Once I upgraded to the current release, Pro Pack loaded and activated without the Fatal Error message.