It sounds like you are storing the text value of the store name in your details table, rather than the primary key value of your stores table
i.e.
Code:
tblStores
S_ID S_Name
1 Store A
2 Store B
3 Store C
tblDetails
D_ID S_Name ----> other details related fields
1 Store A
2 Store A
3 Store B
when what you actually want is something like:
Code:
tblStores
S_ID S_Name
1 Store A
2 Store B
3 Store C
tblDetails
D_ID S_ID ----> other details related fields
1 1
2 1
3 2
You want to sore the primary key field in your details table, NOT the text value of the store. Assuming you are using an autonumber as your primary key you can fix your data by creating a numeric field on your tblDetails table and updating it with a looked up primary key value from your stores table, then your lookup should function properly on the numeric (primary key) field without issue.