Trouble creating Data Service


I just started playing with App Designer but I'm having an issue creating a Data Service. I'll run through the steps I'm following:

To start I'm calling the Mingle User detail service to get info about the current user. I chose this service because it is simple, it returns a single row of data and requires no parameters.

When I test the Data Service I get the following data back and all is good.

At the next screen I first click VIEW JSON and set the root to $.UserDetailList[0]

Here is a sample of the Json:

"Status": 1,
"ErrorList": [
"Code": 1,
"Message": "text",
"Severity": 1
"UserDetailList": [
"Email": "text",
"Title": "text",
"CDNUrl": "text",
"Status": 1,
"UserId": 1,
"LastName": "text",
"PersonId": "text",
"UserGUID": "text",
"UserName": "text",
"FirstName": "text",
"UpdatedDate": "1985-04-12T23:20:50.52Z",
"ProfilePhoto": 1,
"IFSUserStatus": 1,
"IsColemanUser": true,
"IsExternalUser": true,
"EmailPreference": 1,
"ProfilePhotoPath": "text",
"IsTrailModeEnabled": true

I click "Save" to exit the JSON Preview screen. Then I click "Generate parameters" and remove some unwanted output parameters.

I then click "Test Data Service" which pops up a dialog

I click run and it fails. 

 I then played around deleting parameters randomly and I can find a pattern or specific variables causing the problem but as soon as I get down to 6 parameters it works! Is there a restriction on the number of output variables?