Star Base Modules

In GC3 there was a limit to the number of star bases you could built without researching something to raise the limit but you could build as many modules on each star base that you wanted as long as you had the resources and had researched it.  In GC4 there seems to be some kind of a limit to the number of modules you can build on your star bases.  I had enough resources but it gave me an error message that I did not have enough modules.  What do I need to research to raise the limit on the number of modules I can build on a star base?

To give you some feedback, limiting the number of modules you can build on a star base isn't a good thing.  I am competing with multiple civilizations.  I am already resource and technology limited.  I don't need another limit.  Also, having to put a citizen on a constructor in order to build a star base isn't good.  It limits the number of colony ships and constructors you can build.  In GC3 you only had to put citizens on colony ships not constructors.  I think that is a better approach because population grows slowly especially early in the game.