I installed Mathematica 9 on my Windows 7 system (installed the font patch afterwards so the BSOD are gone) but the "Extras" package installation fails claiming it can't de-install the Mathematica 8 packages.
I de-installed Mathematica 8 and tried re-installing Mathematica 9 again but it keeps claiming the Mathematica 8 add-ons can't be removed. At the end CDF (amongst other stuff?) is not working in the browser.
Any thoughts?
I fixed the problem by de-installing Mathematica 9. Then I re-installed Mathematica 8 which gave an error message about the deinstall msg fle not being present. However the installation continued. Then I de-installed the extra package through the control panel (with windows) first and then de-installed Mathematica 8. After that I removed all directories described at http://support.wolfram.com/kb/4730 Then I reinstalled Mathematica 9 (with the latest package). No more errors! However the CDF browser plugin is only installed for Chrome. No idea why because IE is my default browser. I suppose I can install the plug-in for IE from the Wolfram site but I'm doubting if it's not better to wait a bit.
.dmgimage includes the installer includes a separate item "extra packages" $\endgroup$.dmgimage includes, alongsideMathematica.appitself, an `Extras.pkg" for installing the browser plug-in and indexing add-on. For Windows, and this was for Mathematica 8, after you ran the installer for Mathematica itself, you were then prompted whether to install the extras. $\endgroup$