Specifically the error occurs in the Resources.Designer.cs:
Error 2 The namespace \'ModulusFE\' already contains a definition for \'Sto
This is an old question but I didn't find the fix I used, so I've added it here.
In my case it was a namespace with the same name as a class in the parent namespace.
To find this, I used the object browser and searched for the name of the item that was already defined.
If it won't let you do this while you still have the error then temporarily change the name of the item it is complaining about and then find the offending item.