Updating form field Acrobat 9.0

i'm programming in visual basic , i'm able read form field when try update it's value, nothing happens. code works fine in acrobat 7.0.

 

 

set f =jso.getobject("fieldname")

 

f.value = "new value"

 

the field updates fine in acrobat 7.0, nothing in acrobat 9.0. acrobat 7.0 has been uninstalled on machine , acrobat 9.0 installed. can read existing field values, code line doesn't work in 9.0. doing wrong?

on same form worked in acrobat 7?  or new form?  acroform or xfa-based form?

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