How to get rid of “The solution you are trying to open is bound to source control” message

You need to clean the solution file (.sln) by removing the following GlobalSection:

GlobalSection(TeamFoundationVersionControl) = preSolution
    SccNumberOfProjects = 2
    SccEnterpriseProvider = {4CA58AB2-18FA-4F8D-95D4-32DDF27D184C}
    SccTeamFoundationServer = http://example.com/tfs/defaultcollection
    SccLocalPath0 = .
    /// --- more solution specific stuff omitted --- ///
EndGlobalSection

and you need to remove the source control references from every single project file (.csproj for C# projects):

...
<SccProjectName>SAK</SccProjectName>
<SccLocalPath>SAK</SccLocalPath>
<SccAuxPath>SAK</SccAuxPath>
<SccProvider>SAK</SccProvider>
...