This issue could occur when you have recently had a resynchronisation of 'Master Data' from your Financials Database(s) to Capture.
This is where a particular Supplier or Sub Ledger was not exporting from Financials to Capture.
To check, take a note of the Track ID from the Invoice Document you are getting the error on.
Click on the Batches button at the top of the ribbon (where you can see 'Start' and other buttons).
Locate the same Track ID on this view.
Select the row, then click Start.
If you're then prompted with the following error: 'The buyer that was used to upload the document has been deleted'.
This would indicate the Invoice you're trying to verify was uploaded prior to a complete resynchronisation of 'Master Data' from Financials to Capture. A resynchronisation 'Deletes' Buyers and Suppliers data in Capture and sends a new synchronised data up to Capture.
For any Invoice documents presenting this error in Capture you would have to re-upload the Invoice to Capture and delete the original one(s) with the error.
If the issue remains, please see the following Get support in Access Capture and reference the title of this article and please include details of what has been tried.