Dokuwiki comes setup for security on apache servers. So, the problem may be the apache setting for the AllowOverride directive. The Dokuwiki document on
setting apache up for Ubuntu describes the problem. On a dedicated server, you can make the necessary changes yourself. In a shared hosting environment you may be able to ask the tech staff to make the necessary change for your dokuwiki directory.
See also:
http://httpd.apache.org/docs/2.2/mod/core.html#allowoverride