Error opening Data Entry Form Template

When a Data Entry Form template is dragged into the designer window nothing happens.

This error is common when the template is designed by someone else.

1. The first time you drag it in, everything is fine.
2. You make some changes and/or save it.
3. Second time you drag in the template it is not added to the designer.

Output in the Console log:

[freeform.ComponentDropTargetListener] line:279 - 
java.util.concurrent.ExecutionException: java.lang.NullPointerException

Caused by: java.lang.NullPointerException
	at com.fgm.freeform.component.CheckBox.addSiblingKeys(CheckBox.java:215)

This error example is caused by the Data Entry Form template contains a checkbox which has options that do not exist in your database.

4. One way to identify which data field gives the error is to publish the template and then the missing enumvalues in checkboxes will be listed.
5. A more time consuming method is to start with the original template:
1. Delete all data fields on the last page.
2. Save template with new name.
3. Drag it again.
4. Repeat until you have identify which page the problematic field is.