If the issue is isolated to the STORE database I am somewhat unsure how performing or attempting to perform maintenance on the HQ database, would resolve an issue with STORE? You mentioned one of the stores, which sounds like other store databases previously exported successfully for you. So if that is correct, the issue is not with HQ DB at all. The issue is with the store that fails to connect yes? It sounds like in order to correct the connection error you are attempting to export another database?
1. What is the connection error?
Instead of using the sample perhaps this will work.
Open administrator log in with your SA and before connecting to a database or sample try MASTER. (type the word master into the database names)
Connect to the master database so you see master on the bottom of the screen connected.
Then once master is connected try to restore the stores database that is giving you the issue from a backup and see if it gives you any difficulties. If there is an issue within the tables on this stores database? Causing the ERROR 0. (It would probably not allow you to restore).
If it allows you to restore without error (do not name the database the same as before by the way in this process pick a new name) then the connection issue is perhaps not related to the stores database at all? If the other stores databases exported and connected successfully it likely isn't HQ it is "this store".
Have you also updated your SQL to SP 3 as I suggested as of yet?
Thanks, I hope this helps.