Just to go into more detail from my prior post...

If Library1 has a project reference in VS to Library2. And Library2 has a direct reference to "Library1.dll" (the output of Library1), then Library2 will almost always be built against an out-of-date Library1.

  • If Library1 is being built than VS will require Library2 to build first since there is a Project reference.
  • Library2 will then copy over the already existing Library1.dll from the last time Library1 was built and do compilation checks against the classes and method difined in the old version of Library1.
  • Then Library1 will be built against the new version of Library2.

If something were to be changed in Library1 that should cause a compilation error in Library2, I don't think Library2 will catch it until the 2nd time it is built because the 1st time it would be using the "library1.dll" from before the changes were built.