There have been a lot of problems with the ECL wiki, one of them related to authentification. In the end I have managed to create a new wikispace using SourceForge's resources. This should solve most problems, since users who want to edit content in the wiki must just get a valid SourceForge account.
The new wiki is here: http://ecls.wiki.sourceforge.net/ I have already moved some pages. The other ones have been superseded by the newer manual which is now linked from the main page. This manual documents ECL, the library, internals, embedding ECL and extensions, but there are many parts which still need revision, as I have not had time to work on this for the last five months.