pxsetup is part of Music Match software, what it has to do with LR I have no idea. Error 2753 is commonly seen after a system problem, when recovery of the system is done and missing programs are installed again so perhaps the Music Match software instillation file is soem how interfering with the LR instilation.
I have no Music Match installed on my system, so it
has nothing to do with this program.
Thanks for answering my query. Any more suggestions?
It looks like the Adobe developers may have re-introduced an old bug. See here.
My guess is that the old solution will probably apply: uninstall LR 2.5 first.
Also, you might want to search your system disk for that exe. There's one in the Lightroom 2.5 directory, but there may be one associated with MusicMatch (which might have come pre-installed on your computer or tagged along with some other piece of software). If you find it, getting rid of it can't hurt and probably would help.