Hello Akira,
Form Manager has an annoying habit of changing the root tag of your form to something else (I don't remember what). So, when you use a SOM expression that starts at the root like form1.whatever.whatever it fails. To find out how Form Manager is changing your data DOM, add a button to your form with this script on click:
xfa.host.messageBox(xfa.datasets.data.form1.Page1.saveXML("pretty"));
Look at the root tag. I would do this for you, but I don't have an environment with Form Manager handy at the moment.
Once you know what name FM gives your root tag, you can change the root tag of your form to that to avoid this sort of surprise. Another workaround is to never access objects using the full absolute SOM path from the root. Instead use a relative path like this.parent.parent.OtherSubform.whatever...
Please post a followup to tell me if that solved the problem, and tell me what FM changes the root tag to. It's bugging me now. Thanks.
Jared Langdon
J. Langdon Consulting
www.jlangdon.ca