The process of migrating Joomla 1.5 to 2.5 is often a complex process, depending on what extensions you have on your current website. It's seldom a one-click process.
First of all, make sure you have a complete backup of your site (I recommend Akeeba Backup)
There are several ways to do the migration, and several tools that claim to be a one-click solution. As you see, that doesn't always turn out to be true. I'm going to list a couple of alternatives, but first keep in mind the following:
- Your current template will probably not work with Joomla 2.5. You'll have to:
- modify it to make it compatible
- download a new version from the template provider (if available)
- use a different template
- You'll have to look for an upgraded version of most of your extensions.
- Some of your extensions might not be available for Joomla 2.5, and you'll have to look for an alternative extension with similar functionality.
(on a side note: Joomla 2.5 has a planned End Of Life in a few months, you might want to consider upgrading to Joomla 3.)
Option 1: Build a new site
Taking into account the points above, you might be better of creating a completely new site. Start with a clean Joomla 2.5 (or 3) installation. Then use J2XML to transfer your articles (with images), categories, menus and users. This will give you a kickstart, and the advantage is that you have a very clean Joomla installation. Install a new template and configure the site as needed.
Option 2: Try other migration tools
If jUpgrade fails, there's a list of different tools for Joomla migration at JED. You might have better luck with another migration tool. As long as you work on a copy of your site, there's nothing wrong with testing different solutions (except it might be time consuming).