Installing on a PC that had never had a EA installed.
I uninstalled SQL Prompt 3 & 4 and Refactor 1 (didn't realise the latest installer would attempt to remove Refactor).
Ran the installer from the Download Complete prompt from IE.
Installer ran through, showed an error message indicating couldn't write to C:\\Program Files\\Red Gate\\SQL Prompt 5.
Windows (7, Ultimate, 32bit) displayed the usual "this program didn't install properly, would you like to try with recommended settings" message.
On retry, successful.