.NET - multiple DLLs and one namespace
It is indeed better component design as @Tyriar mentioned, but it is also very common that the namespaces are being used among the projects. This is not always a wrong design.



Let assume that you are implementing plug-ins. And every plug in has own assembly (normally). There, namespaces can be shared. 

PluginA.dll

Namespace CompanyName.SolutionName.ProjectName.PlugInNamespace
{
    Class PlugInA {}
}


PluginB.dll

Namespace CompanyName.SolutionName.ProjectName.PlugInNamespace
{
    Class PlugInB {}
}




Better practice for your case would be the sub-namespacing.

ClassLibrary1 

Namespace Com.App.Test.FunctionalityGroupA
Public Class Class1

End Class
End Namespace


ClassLibrary2

Namespace Com.App.Test.FunctionalityGroupB    
Public Class Class2

End Class
End Namespace


WindowsApplication1

Imports Com.App.Test.FunctionalityGroupA
Imports Com.App.Test.FunctionalityGroupB  

Public Class Form1
    Dim c1 As Class1
    Dim c2 As Class2
End Class