I Had a similliar problem and I couldn't sort it out. I just installed my poser to a new, different location and added my old runtime to it as an external runtime. That way I was able to acces all my old files.
I think you may be better of installing your poser to a different location. Use the current poser runtime as an external runtime. First  a fresh new instal to a different location and then use your old poser runtime as an external runtime. Or a fresh instal and then copy paste your old runtime to your new poser runtime and overwrite it. Confusing enough? It was for me. But I got it working. Well I'm upragding my system in a couple of days time and I have to go through all that again. :S

-Morbo will now introduce the candidates - Puny Human Number One, Puny Human Number Two, and Morbo's good friend Richard Nixon.
-Life can be hilariously cruel