A long time ago (back in the ReSharper 2.0 days), I filed a bug about the lack of support for custom ASP.NET BuildProvider's within ReSharper. The bug is RSRP-25954. I was quite elated a couple weeks ago when I got an email from the tracker saying the bug had been fixed on version 4. Today I finally got around to trying the latest EAP build (777), but unfortunately, it seems it has not been fixed. I have created a very simple sample solution (attached) that repros the fact tha ReSharper is still not recognizing the code generated by the custom BuildProvider. You will note that in the code behind of Default.aspx, the line of code is highlighted in red, when in fact it compiles fine.