NX Unable to Edit/Open Spreadsheet in Part Family.

When trying to Edit/Open Spreadsheet in Part Family, NX is unable because it keeps thinking without result.

After long time waiting an error comes up  'UGXML_dom_not_found_err' 

Check your customer defaults.

Under Modeling-->Part Families-->All--> Keep All Part Family Add-ins in Spreadsheet (on)

After restarting NX, this will make your Part Family Spreadsheet editable.