Like any document, the QRecall application must have permission to read, and probably write, to the archive.
For documents on external drives and volumes, this can sometime be an issue. It can be further complicated if multiple users are capturing to the same archive.
Local volumes—physical drives connected directly to the computer system via an internal (eSATA) or external (USB, Firewire, Thunderbolt, …) bus— are usually the easiest to work with. Just make sure the archive was created by the user running QRecall and everything should be fine.
If an external drive is shared between multiple computer systems, you may encounter ownership or permissions errors when accessing the archive from a different system. That's because different user account identifiers (UIDs) make the document appear to belong to another user.
The simplest solution is to make the external volume an open resource, devoid of ownership restrictions.
In the Finder,
This setting is stored locally for each system, so you'll need to move the external drive to each system that uses it and repeat these steps.
If the external drive is also used for documents that require ownership and permissions, and you can't repartition the drive so that the QRecall archive has its own volume, you need to make sure that all users have read and write access to the archive.
Network (sometimes referred to as shared) volumes pose a similar challenge if more than one user is capturing to the same archive.
The simplest solution is to use an analog of the "Ignore Ownership and Permissions" option used for local drives (see Local Volumes above). Many network file servers (like Apple's Airport Extreme) and NAS devices have a mode where all users are treated the same and have unfettered access to shared documents. Using that mode will make multi-user access in QRecall a breeze.
In the Airport Utility application:
All QRecall users will then connect with the same password and will have equal access to the archive.
If your server doesn't have a "shared" mode the next solution is to use the same remote account to access the archive volume from all client systems. When logging into the server with the archive, use the same account name (and password) on every client system.
If that's not practical, the networked archive will need to be shared using one of the Local Volumes techniques explained above. In other words, you'll need to place the archive in a shared folder on the server, accessible by all client accounts.