This was one I came across recently while doing some custom branding work on a SharePoint 2010 site which was using Performance Point Services, and specifically the PerformancePoint Report Web Part.
I had a simple branded master page (which was a copy of the normal v4.master) but could not for the life of me get PerformancePoint reports to work.
Unterminated string constant
Well .. I rolled my site back to the v4.master and it was working again. I copy-pasted the v4.master <head> contents into my custom master page and it started working again .. although when I double checked the contents they were IDENTICAL.
So far this was very very weird .. and the actual solution is even weirder.
It seems it was to do with my <title> element in the <head> tags being broken onto separate lines:
<asp:ContentPlaceHolder id=”PlaceHolderPageTitle” runat=”server” />
<title><asp:ContentPlaceHolder id=”PlaceHolderPageTitle” runat=”server” /></title>
Why?? I have no idea .. but making this simple change solved the problem.