The path to your data directory should be a file system path, not http://

If you're on windows it will look something like: C:\xampp\dataroot/

If on linux (presumably Mac too?): /var/www/dataroot/

Thanks Matt

The install direcory is D:\Joomla\server\root\el/

When I add the data folder under root (outside elgg) install says "it does not exist" When I add it inside the ellg folder it tells me "Your data directory D:\Joomla\server\root\el/data must be outside of your install path for security"

I tried to modify the htacess, but probbly did it wrong (I can't find the post now). As this seems to be the only viable option, and I'm not familiar with the file I would like to know where and how do I have to  change it.