I got a lot of errors as below with my database project, Visual Studio 2013. However I don't use any of below dlls anymore (I used them before, but I removed them from references).
Error SQL72009: [Accessibility] has an unresolved dependency to 
[System.Windows.Forms]. A deployment script with correct ordering cannot be 
created.
Error SQL72009: [System.Design] has an unresolved dependency to [System.Web]. 
A deployment script with correct ordering cannot be created.
Error SQL72009: [System.Windows.Forms] has an unresolved dependency to 
[System.Web]. A deployment script with correct ordering cannot be created.
Error SQL72009: [System.Windows.Forms] has an unresolved dependency to 
[System.Design]. A deployment script with correct ordering cannot be created.
Error SQL72009: [System.Windows.Forms] has an unresolved dependency to 
[System.Drawing.Design]. A deployment script with correct ordering cannot be 
created.
Error SQL72009: [System.Windows.Forms] has an unresolved dependency to 
[Microsoft.Build.Tasks.v4.0]. A deployment script with correct ordering cannot 
be created.
....
So my question is:
- What exactly does error sql72009 mean?
- When does it happen?
 
    