After the release of Joomla 1.6 RC1, I had come across a significant roadblock in developing a website…. extensions. With Joomla 1.5, there was always the ability to manually insert extensions into administrator and components folders or with the backend installer.
But, with Joomla 1.6, the installer will not install Joomla 1.5 extensions without recoding installers, nor can components be manually dumped into the proper folders and using the Discover setting. The discover setting will pick up the extensions, but the component will not install.
I could only hope these issues will iron out in time, but, in the meantime it looks like Joomla 1.6 has nothing on Joomla 1.5 that has an additional ACL component.