Bulk Insert task can't open file

Question

I have a text file that I'm trying to import through SSIS (running in Visual Studio 2022) with a Bulk Insert Task. I've used it successfully from the same package for other files, but one set of files always gives me an error (Cannot bulk load because the file "..." could not be opened. Operating system error code 3...)

I can open the file in other applications including a text editor. I have quadruple checked that the path is correct. I've checked permissions on the files and granted all permissions to Everyone. I've rebooted the machine in case something was holding a lock on it. Still nothing.

I'm running from within Visual Studio - NOT from a SQL Server, so this shouldn't be a case of the SQL Account not having access to the folder or the folder name not being a UNC path (right?). As I said, other files in the same directory have worked fine.

I'm at a loss at this point - any suggestions on other things that I can check? Any debug methods that I might be able to use?