1. 01

   Review the type and size accepted by the active control.

2. 02

   Confirm that the file is not empty, password protected, or still open by an incompatible process.

3. 03

   Verify the account, project, workspace, or email to which the file belongs.

4. 04

   For a download, open the current notification or link rather than an old bookmark.

5. 05

   In Office, confirm that client and item mode allow the attachment.

6. 06

   Retry with a minimal non-confidential file only when diagnosis requires it.

Practical guidance

Check the active attachment control, file type and displayed state before sending. A selected filename is not proof that upload finished or that its contents were extracted. For downloads, distinguish failure to open the link from failure to open the downloaded format, and retain the exact error without exposing the file contents.

Advanced tips

Use a small permitted file of the same type to isolate a format problem from an access problem. If only one source fails, investigate its protection, version and availability; do not repeatedly upload the entire confidential collection for diagnosis.