This seems to be a universal problem these days. I have seen ZERO reports of success using JUpgrade lately. My try on a simple test site I have - one that uses no extensions other than the standard package, fails the exact same way.
I've seen lot's of complaints about this on other forums. So I thought I'd give it a try on a trivial test site I have.
It leaves a big security problem too unless you clean up after it. The URL:
www.what-ever-your-site-is.whatever/jupgrade is left with the install directory in place, so anyone can then log in to the (empty) new site.
Interestingly the support links under
docs.joomla.org/Migrating_from_Joomla_1.5_to_Joomla_2.5
all fail with a 404.
Oh well, this is turned out to be a totally useless migration tool.
Regards,
Bill