We just tested Forest Pack 6.2.4 in 3DS Max 2015 SP4, and everything seems correct.
Please, try this:
1.- Delete the files ForestQt.dll, QtCore_Itoo_4.dll, QtGui_Itoo_4.dll, QtXml_Itoo_4.dll and QtSolutions_MFCMigrationFramework-Itoo.dll from the 3DS Max root folder.
2.- Reinstall Forest Pack with admin privileges (as described in my previous post). Please also be sure to use the latest version.
3.- Check if the files listed at step 1 are copied in the 3DS Max folder, after the reinstallation. If so, try to use Forest and tell us if it worked.