方法在NHtmlUnit中创建WebClient时未发现异常

我使用NuGet将NHtmlUnit包(v2.15.0.0)安装到使用Visual Studio 2015的MVC5项目中。

var client = new WebClient(BrowserVersion.CHROME);

我也试过不指定浏览器，使用IE11。

以下是例外的详细信息:

System.MissingMethodException occurred
  HResult=-2146233069
  Message=Method not found: 'Void java.util.HashMap.__<clinit>()'.
  Source=HtmlUnit
  StackTrace:
       at com.gargoylesoftware.htmlunit.Cache..ctor()
       at com.gargoylesoftware.htmlunit.WebClient..ctor(BrowserVersion browserVersion)
  InnerException: 

以下是调试器对NHtmlUnit和IKVM.OpenJDK.Util.dll .dll的说明:

Name=NHtmlUnit.dll
Path=C:'Windows'Microsoft.NET'Framework'v4.0.30319'Temporary ASP.NET Files'root'ef1fc9af'43f83bfb'assembly'dl3'362bd10d'0ab5a1ee_d0e5d001'NHtmlUnit.dll
Optimized=Yes
User Code=N/A
Symbol File=Cannot find or open the PDB file.
Order=109
Version=2.15.0.0
Timestamp=7/11/2014 1:23 AM 
Address=0F6E0000-0F754000
Process=[13336] iisexpress.exe
AppDomain=[2] /LM/W3SVC/2/ROOT-1-130857754150438760 
Name=IKVM.OpenJDK.Util.dll
Path=C:'Windows'Microsoft.NET'Framework'v4.0.30319'Temporary ASP.NET Files'root'ef1fc9af'43f83bfb'assembly'dl3'7fc27125'b1c29ef9_d0e5d001'IKVM.OpenJDK.Util.dll
Optimized=Yes
User Code=N/A
Symbol Status:
Binary was not built with debug information.
Order 66
Version=8.01.5717.0
Timestamp=12/31/1969 5:00 PM
Address=0E9D0000-0EAC4000
Process=[13336] iisexpress.exe
AppDomain=[2] /LM/W3SVC/2/ROOT-1-130857754150438760 

这感觉很像。net模块版本不匹配，但我唯一有任何参考或曾经使用过任何NHtmlUnit或IKVM dll的地方是在项目中(它也在干净的机器上复制)。有什么诊断方法吗?