Hi Clay
I have resolved this problem.
The reason for the problem is just as your hint that my database is somehow wrongly mapped.
The datasource in my form is as following:
Main
Group1
Field1
Group 2
Group3
Field2
I mapped the child table to Group 2 instead of Group 3, thus the following colums are mapped with xpath my:Group 3/my:Field2.
When I change the child table mapping to Group 3, and then remapped the fields, the xpath changed to my: Field2.
Would u please give further explaination what's the difference between the above 2 ways of mappings? And why the first mapping caused the problem?
Thank u so much!
Wish u a good day :-)