Jumla installer has become very clever these days. Checks at the beginning of the requirements and if the hosting does not match them – refuses to install. Stupidly lit button “Re-check” and all.
Most often it has to do with the variable register_globals. On many webhosts it is enabled by default.
The solution:
To make the installation happen, you need to rename htaccess.txt to .htaccess and add a line there:
php_flag register_globals off
I hope it helps you 🙂