Visual Studio Build Definition - How to add additional (dll) files to build?

Thank you for your answers. Actually, we studied on it further and found a solution as follows:

• Put dll's into _bin_deployableAssemblies folder under web application (name of this folder is important)
• In the MSBuild Arguments part of the build definition, add /p:ReferencePath=""

That solved the problem. Thank you again in advance.

You can either (#1) make these 3rd party DLLs available in the server that does the build, or (#2) check them in into the source control.

This is a discussion that has occurred several times in the past, in general the most advisable thing to do is proceed with option #2 .

Here are some further similar questions in SO, that might be useful to you:
How to deal with external assemblies
Team Build 2010 - Third Party Assembly References not copying to output folder
Visual Studio Package build and DLLs in private bin path

You will need to add the files into the Source Control repository. In our solution we have a \3rd Party folder that contains all of the 3rd Party assemblies that our projects references.

\Main
  \3rd Party
  \Application
  \Modules
  \etc.