Symptoms

Page or blog titles with spaces won't work when How to setup Confluence with IIS.

Cause

The IIS7 request filter rejects URLs containing + characters due to its security setting.

Resolution

Turn off the doubleEscaping feature for Confluence, for your site or for the whole server. Here is an example:

%windir%\system32\inetsrv\appcmd set config "Default Web Site" -section:system.webServer/security/requestfiltering -allowDoubleEscaping:true

See also Microsoft's knowledge base article.