As you can see, you connect four tables with the field "key".
The Link-table has the fields date, datetype and three different number fields EN-Enquiry_No, NB_Enquiry_No and RN_Ref_No. These fields are also in three of the other tables, which are linked with the field "key". The field names are identical, so qlikview connects them automatically.
Replace them to the field key so that your Link table has only three fields: date, key, datetype. Then your Link-table is also only connected to the other ones with the field key.