Please note: for browser security reasons if you wish to change the image file, you may need to browse and select it again.
This error currently occurs when the 'File' Attribute is hidden in Admin > Attributes.
You can view hidden attributes by clicking on the 'View hidden attributes' link at the bottom of the page (Admin > Attributes).
Until we fix this in a new release of Asset Bank please make sure that the 'File' attribute is not in this list (click on [show])
After you have 'unhidden' the attribute you will need to [reindex existing items].