As you may know, it is possible to migrate a DSL Project to the current version of Visual Studio using DslProjectMigrationTool.exe which is available from the Visualization and Modeling SDK. This is no exception for Visual Studio 2010, where the tool can be found under Microsoft Visual Studio 11.0\VSSDK\VisualStudioIntegration\Tools\DSLTools with Microsoft Visual Studio 11.0 is the installation folder for Visual Studio 2012
I has been reported that, in rare cases, some migrated DSL projects may exhibit the following issue: the DSL package project does not compile due to an error in the DslPackage\GeneratedCode\Package.cs file caused by an undeclared namespace alias
There is an easy workaround:
The project will then build correctly.