Working on a site that is not public yet we upgraded to 1.6 in the past few weeks. When upgrading we had a problem where the "add elements" to the template stopped working. We documented it well in this topic.
We found a solution by deleting the theme choices completely and reloading it.
However, now the following "JSON data from server could not be parsed. This is caused by a JSON formatting error" is displayed when you enter the backend going to the dashboard. One of our people continued development since we were almost done, adding widgets. That all worked fine except for this error when she went into the backend.
Then I had her start working on the last item, the home page. To do that she need to add images to the slide show on pages we would want to show up in the home page with links. When opening any page to edit and "add image to slide show" the page the gets grayed out. You can not add an image or edit anything.
I did shut off all plugins, and I can now add the image without the error. I do not get the JSON error when going into the backend. I am now adding them one by one to see when it fails. I will report back when I have more data.
However, I added no plugins since upgrading to 1.6 all we did was upgrade choices.
Is this related to the JSON error?
What is JSON?
When the incomplete install, the installation that had the first error in the "element details" happened, did that corrupt our database somehow?
How do I solve the error, and at the same time not loose what we have done?
Create a new thread and tell me what problems you are encountering and what you want to know. 
There is no step 3 :) 
