While I was modifying SharePoint’s master page to put an inline code, I was constantly redirected to SharePoint Error Page “An unexpected error has occurred”.

After spending nearly an hour to get a clue from EventLog and other sources, I found out that by adding the following config codes to web.config of the web application where the site collection resides, we can see the ASP.NET error page with detailed information.

<SafeMode MaxControls=”200″ CallStack=”true”>
<customErrors mode=”Off”/>