Update Query issues

[Grimmers]

I have a membership db that occasionally needs to swap members between memberships such as marriages of 2 members. I have just set up a form to select the member from a list box, put the new membership number in a text box and run an update query to change the membership number. The membership number changes, but it also adds a new row, memberID and new MembershipNo, to my members table. Apart from deleting the new row in a new query I don't know what I have done wrong.

My update statement is:

UPDATE t_members SET t_members.lngMembershipNo = Forms!f_memchange!NewMem WHERE (((t_members.lngMemberID)=[Forms]![f_memchange]![MemList]))

Could somebody please shed some light on this??

cheers,


David