I had this error:
The ConnectionString property has not been initialized.
I have a MSI installer, that is installed in our QA environment.
It was working before, and suddenly, I only had this error.
Googled up a bit, all this info on how to get the connection string and all that.
I finally realized that I rebuilt the whole solution, but I didn't rebuild the Deployment project. After a rebuild ... everything back to normal.
Hope this helps someone.