Question : Field in subform locked but Locked=No

Access 2000. Subform reads recs from a table linked to the table the main form reads. (one-to-many). Typical Order Entry form with order header info in main form and line item details in subform. When focus moves to the first field in the subform (which is the only field that is not locked or display only), the field behaves like it is locked and the user cannot enter a value. The fields properties are enable=yes, locked=no. Any ideas on why or what I could look at to see why this is happending. I didnt write the orginal code but I can't find any VBA modules attacahed to it or macros either.
Any help would be greatly appreciated. THX! :)

Answer : Field in subform locked but Locked=No

Or the subform could be locked.  Check the recordset of the subform and see if that is updateable.