Code blocks are not allowed in this file ppssample.aspx

Well this is a new one.  I've done some MasterPage customization for our SharePoint site.  After installing a Business Intelligence site, I tried to start up the Dashboard Designer by clicking the "Start Using PerformancePoint Services" link on the homepage.  Rather than it starting, it freaked out, telling me "Code blocks are not allowed in this file ppssample.aspx".

Fortunately, I have debugging mode turned on in SharePoint, so I received a yellow screen of death.  The yellow screen also shows the link it was trying to open, which is

var designerRedirect = "_layouts/ppswebparts/designerredirect.aspx";

So, on a whim I tried http://mySharepointSite.com/sitename/_layouts/ppswebparts/designerredirect.aspx, and wouldn't you know, the designer opened.

Apparently, once you use a customized version of a MasterPage, your custom MasterPages run in a partial trust safe mode that blocks certain functionality.. including (you guessed it) code blocks.

So you can revert your business intelligence site back to an OOB MasterPage, or try opening the designer using the method described above.