Hello Richard we had this issue in the past and found that it was usually permissions issues on fields you are mapping within the manage package. A good way to find the root cause of the issue is in your browser window hit F12 to bring up browser console. If it is a permissions issue then browser console will give you the field it is erroring on and you can fix it.
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Sheldon Breading-Goodrich
Edelman Financial Engines, LLC
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