Quote - 3) P:Program FilesSmith MicroPoser Pro 2010. But I just tried to install V4 to this path again And I chose Poser (All Files) when asked for the target application and I got a message stating that "When used with Poser TM, "Victoria 4.2 Base" must be installed to the same directory as the application executable; due to restrictions on support file locations."

You may be getting this message because I think the installer only looks for Poser.exe and not PoserPro.exe. If you make a copy of the PoserPro.exe file and rename the copy Poser.exe, V4 will probably install okay.