Subject Invalid class typecast

I am new to both Interbase and IBO. I have set up a simple form that
has a TIB_Connection, TIB_Transaction, TIB_Datasource, TIB_Query,
and a IB_Edit. I believe I have all the necessary properties set
correctly. I can connect to the Database etc. just fine. The
problem I have is when I try to set the Datasource and Datafield
properties in the IB_Edit. I can select the Datasource from the drop
down menu but when I try to set the Datafield I get the
error "Invalid Class Typecast". I get this error when I try to
select the drop down menu. If I try to type the fieldname I get the
error after each character typed. However, once I have the correct
fieldname entered and run the program, the IB_edit works fine. If I
go to the Basic Tutorials and bring up Tutorial 4 I get the same
error when attempting to set the property on the sample form. I just
downloaded IBO yesterday so I assume I have the latest version. Can
anyone help ? Thanks.