It could be several different things.
If it is a binary reference from NuGet then simply opening the solution should download the correct version. You can look for a package.config file in the solution root for this.
If it is a binary reference but not from NuGet then there is no way to know the version. You can open the project file in a text editor and, most likely, it'll have a hint path that specifies where the original version was from but that does you no go by
itself. Since you're downloading from TFS it sounds like this is private code so it is possible this solution requires that you also download some sort of shared source code from TFS as well. Only your company devs would know that so you should ask them.
If it is a project reference then it is most likely missing from TFS. But again it could be a shared project and you would also need to download it from TFS. Your company devs should be able to answer that.
Michael Taylor http://www.michaeltaylorp3.net
