GL Accounts did not Import with Inventory Items
Before you Import Inventory Items make sure to set the Default Plant Location and Default Price Level in Admin -> Inventory Setup -> Genreal Setup. If the defaults are not set the first location and price level found will be updated.
Now re-import your items and the GL Accounts will fill in.
Advanced users with knowledge of the database can run an sql query to set the proper GL account for your items. Look at a recent entry in the item table. Update the following fields for all your items to give them the same value:
update item set inventoryglacctid='xxx', salesglacctid='xxx' where companyid='1';
This will update all your items with the same gl account.