If you’re running ownCloud on a server with FCGId you might wonder why login to the web interface work flawlessly but your sync client keeps saying that the provided credentials aren’t correct.
The problem is, that the webdav auth done via remote.php (this is actually used by the sync client) is not able to process the credentials because of FCGId.

The following .htaccess in the root folder fixed this problem for me, you need to enable mod_rewrite for this to work.

<IfModule mod_rewrite.c>
RewriteEngine on
RewriteRule .* - [E=HTTP_AUTHORIZATION:%{HTTP:Authorization},L]