MC Access Join Key & Recordset QU

Hi!
I've created DB in MS Access. It contains datas about school. I've made query that retrives data from 3 tables: Professors, Classes and Subjects. They all have primary keys ( ID...) and those data as foreign key in related table, and beween Classes and Subjects I've formed a index table containing ID from both tables as foreign keys.
But, when I make Form that should update some of datas conected with Profesors, I can't do it because some of feelds give me error message ( in sttus bar) " Join key not in Recordset.
How can I reach property Recordset and affect it?

Check the data you are trying to enter in your Classes or Subjects table. Chances are that you are entering primary key data that do not exist in your Professors table.

Make sure that first you enter all your master data in Professors table then enter data in Subjects/Classes table. You should use combo box for such requirement which fetches data from Professors table. This will avoid such errors.

Here Professors table is master table which can have related multiple records in Subjects/Classes tables.

Also you should create Relationship between the tables. Go to Tool->Relationship on the Access 2000 menu bar.