I'm guessing that you want to upgrade it by clicking link in Socialize template... then you're redirected to Joomla! upgrade list page.
Then you have issue with error notice.
T3 plugin is developed and hosted by T3. It seems that they have issue with xml file so upgrade ends with failure.
You need to:
- contact with T3 developers
- or download T3 plugin and install it via Joomla Installer
- Instead of saying: 'it's not working', explain the problem in detail.
- Screenshots with the URL visible in them and the problem marked are more than welcome.
- Tell us how to replicate the problem, we can't fix it if we can't find it.
- Make sure that your site/server meets JomSocial System Requirements
- Make sure to setup JomSocial Cron Job
- Always provide us with access details to the backend and ftp. We need it to debug problems.
- If you have a similar problem, but a solution you found isn't working, open a new thread instead of 'merging' with an existing one.
- Use the "Thank You" feature on any post that helped you
