You have Microsoft SQL Server Data Tools (SSDT) - Business Intelligence for Microsoft Visual Studio 2012 installed on your computer.
You connect to the Team Foundation Server (TFS), and then you open the source control browser in SSDT.
You try to create or open an Analysis Services Tabular project in the same instance of SSDT.
In this scenario, you receive the "Class already exists" error message.
Cumulative update information
Cumulative Update 4 for SQL Server 2012 Service Pack 1
The fix for this issue was first released in Cumulative Update 4. For more information about how to obtain this cumulative update package for SQL Server 2012 Service Pack 1, click the following article number to view the article in the Microsoft Knowledge Base:
2833645 Cumulative update package 4 for SQL Server 2012 Service Pack 1
Note Because the builds are cumulative, each new fix release contains all the hotfixes and all the security fixes that were included with the previous SQL Server 2012 Service Pack 1 fix release. We recommend that you consider applying the most recent fix release that contains this hotfix. For more information, click the following article number to view the article in the Microsoft Knowledge Base:
2772858 The SQL Server 2012 builds that were released after SQL Server 2012 Service Pack 1 was released
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.