After releasing ASP.NET and Web Tools 2012.2, which is also included in Visual Studio 2012 update 2, we’ve received a few customer feedback about their VS shows an error dialog saying:
An exception has been encountered. This may be caused by an extension.
You can get more information by examining the file 'C:\Users\<username>\AppData\Roaming\Microsoft\VisualStudio\12.0\ActivityLog.xml'.
When looking at ActivityLog.xml, the following error message may show up:
System.ComponentModel.Composition.ImportCardinalityMismatchException: Duplicate EditorFormatDefinition exports with identical name attributes exist. Duplicate name is LESSCSSVARIABLEDECLARATIONCLASSIFICATIONFORMAT
To solve this problem, one just need to update the “Web Essentials 2012” extension to the latest version.
What happened is author Mads (also PM in the Web editor team) graduated LESS and CoffeeScript feature from web essentials 2012 and put these feature officially in ASP.NET and Web Tools 2012.2 (see change log for version details). So using an old version of Web Essentials will conflict with the newest version of VS2012 update 2.
Thanks for the support! And keep enjoying Web Essentials!