UAC is overly protective and Poser needs access to its files and overwrite them. I had problems with Poser 7 and things acting all wonky until I followed Laurie's advice to get Poser out of Program files and have actually found features that were inacessible before finally working.

Also I had most of my "Content" installed to MyDocuments/PoserContent rather in the main Runtime. I believe Poser 8 already puts the content files in MyDocuments... Right?