SSIS 2012 Method not found: void

I ran into this same issue on a computer with Visual Studio 2010 (although I'm sure VS2012 will have the same resolution). I installed Visual Studio 2015 and then started receiving this error when I tried to open an ADO NET source or an OLD DB Source in VS2010. I found that my DatatransformationServices files in the folder C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies had become corrupt. I copied all Microsoft.DatatransformationServices files from a computer where VS2010 was working to my local computer, folder C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies.

You can use a command like the following from cmd to do so:

copy /Y "\\\GoodComputerName\C$\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.*.dll" "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\"

I then added the assemblies to my cache using the following commands in cmd (just change the directory with gacutil to your newest version in the folder C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin and change the folder for Visual Studio to the folder for the version in which you are receiving the error):

cd "C:\Program Files (x86)\Microsoft SDKs\Windows\v10.0A\bin\NETFX 4.6.1 Tools"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DatatransformationServices.DataFlowUI.dll"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.Design.DLL"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.DTSExecUI.Controls.dll"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.Interfaces.dll"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.VsIntegration.DLL"
gacutil /if "C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DataTransformationServices.Wizards.DLL"

I just fixed the same problem with CCleaner free version by fixing broken registry entries.

For me, the problem occurred in SQL Server Data Tools 2012 which uses Visual Studio 2010 after installing multiple versions of SSDT including the 2015 Preview.

Opening any OLEDB source component raised the missing DLL error for C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\PrivateAssemblies\Microsoft.DatatransformationServices.DataFlowUI.dll

The solvusoft.com site linked by GoldBishop provided useful information about the problem but recommends using their dubious product to fix it. Please read this thread on the Norton community site regarding Solvusoft and how it uses RegCleanPro.

Before using a tool like CCleaner, please research it. See who has rated it as a good product. While using it, check that it has backed up your registry entries (it does).