I don't think that here is any prospect of future compatibility between Transposer and Poser 7, so, if it is Poser 7 involved here, that is the reason.  

I do find the dreaded "unknown error" a bit annoying in Carrara.   I don't think  I have ever yet seen a "known" one.   Once the unknown errors start, I think you have to kill Carrara and start again.