Lots of C#.net 2008 projects in one solution file

Question

C# project questions:
1. In a C#.net solution that was maintained by a team of programmers, is there a way to tell how to get the build to locate no errors when it is compiled. Basically I would like to know the order of items to try to get a large solution to compile.
 **I am asking that question since the programmers that worked on this large application have moved on to other programming teams in the company. I am told that this C#.net 2008 application did compile clean 6 months ago and no changes have been made to the application.
  Basically are there some suggestions you have on what to try to get the compile errors/warnings to decrease?
2. How can you tell the manner of how different projects within the same solution communicate with each other? Basically are delegates used,linq, DLLs, used?