Couldn't install new theme in Joomla! Why is that?

Most likely it is a compatibility issue. Are you sure that you are using a template that is compatible with the version of Joomla you are running? If you have a 2.5 site 1.5 templates won't work. Sometimes 3.0 templates may not work with 2.5 sites.

Other than that there is also the possibility that the file needs to be unzipped before you upload and install. Sometimes developers package multiple versions of a component, template, or module in one big zip file and you have to unzip and then use the one that matches your joomla version.

If you are sure that it is neither of these problems then unzip the package and upload them all to your /templates folder. Then go into extensions->Discover and tell it to discover anything missing. It will look through the folders and find anything that has not been properly installed.

If that doesn't work then my advice would be to find a different template.

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