There is a new version of diasymreader.dll, only the Visual Studio is loading version 10. Maybe they changed the interface that you are using:
diasymreader.dll C:\Windows\Microsoft.NET\Framework \v2.0.50727\diasymreader.dll N/A N/A Exports loaded. 63 8.0.50727.4927 (NetFXspW7.050727-4900) 04.06.2009 09:24 05200000-0528D000* [5028] venhance.exe: Native diasymreader.dll C:\Windows\Microsoft.NET\Framework \v4.0.30319\diasymreader.dll N/A N/A Exports loaded. 202 10.0.30319.1 built by: RTMRel 18.03.2010 14:10 570D0000-5717A000 [5312] devenv.exe: Native Jan -- -- mono-cecil