I used V3, SR1, with the Catsuit, SR1.

Sometimes copying and pasting is kind of finicky. Make sure you click on Other, and only once, so it's highlighted, before you do the copying and pasting.

I really like the UltraCatsuit, and generally don't have problems using it in Poser 5. I don't understand why it's working for you, too. :-( I'm sure anything made by Billy-T is worth the money, but you shouldn't have to buy all new clothes just because you've switched to Poser 5.

Also, much as I admire Billy-T's work, his clothing usually doesn't include any morphs. Looking at his Body Suit, it says it doesn't fit the standard V3. So it may not fit your characters, either.