Construct makes an indirect reference

Code:

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Error        3        Construct makes an indirect reference to project 'SInterfaces',
which contains 'S.IUnsolMsgData'. Add a project reference to 'SInterfaces' to your project.
 This error could also be due to mixing a file reference with a project reference to
assembly 'SInterfaces.  In this case, try replacing the file reference to 'SInterfaces.dll' in
project 'SIOTransit' with a project reference to 'SInterfaces'.       
C:\Source\SFramework\Framework\SIOTransit\IOTransit.vb
        1048        21        SIOTransit

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Thanks for your help.

You havent asked a question, you havent even described your situation. All you have done is post a message that tells you exactly what to do. What are you expecting us to say? Have you done as the message tells you to do?

I don't understand this sentence.

Code:

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Add a project reference to 'SInterfaces' to your project.

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It is unclear. Add something to the 'SInterfaces' project???

No, the other way round. Add SInterfaces to your project - well a reference.
Go to the Project menu in Visual Studio and then go to Add Reference and find this SInterfaces reference in the relevant tab in there