A World Wide Web browser, such as Windows Internet Explorer, is required to use this feature

Start > Run > C:\Windows\System32\ComputerDefaults.exe > Select the 'Custom' radio button and click the chevron to the right > Choose a default web browser: 'Internet Explorer' radio button > OK

SP2010 - web.config debug settings

inetpub\wwwroot\wss\VirtualDirectories\80\web.config
14\TEMPLATE\LAYOUTS\web.config
14\CONFIG\web.config

<configuration>
  <SharePoint>
    <SafeMode CallStack="true" />
  </SharePoint>
  <system.web>
    <customErrors mode="Off" />
    <compilation debug="true" />
  </system.web>
</configuration>