"Could not upload the file to Confluence. The server may be unavailable" via Insert Link dialog

[sai surya]

Hi everyone,

I recently upgraded my Confluence DataCentre instance from 9.2.x to 10.2.0. Everything is working fine post-upgrade, except the link file.

When editing a page and using Insert Link → Files → Browse to attach a new file, the dialogue displays:

Could not upload the file to Confluence. The server may be unavailable.

However, the file does get uploaded. If I close the dialogue and reopen Insert Link → Files, the file is in the attachment list. It may be a timeout error rather than an actual upload failure.

Checked the Base configured URL and it matches exactly with the URL that I am using.

[Christos Markoulatos -Relational-]

Hi @sai surya 

The current Atlassian support KB for this on Data Center points to a few likely causes: a mismatch between your configured base URL and the URL used in the browser (even subtle differences like a missing port or context path), antivirus software like Symantec Endpoint or Trend Micro running on the Confluence server and interfering with uploads, or an HTTP 400 on batch.js calls visible in your browser's network tab during page load. It's worth opening developer tools, loading the edit page, and checking the Network tab for any failing batch.js requests before you do anything else, as that will quickly tell you if there's a routing issue. Also check atlassian-confluence.log immediately after triggering the error and look for anything referencing attachfile.action.

One thing worth noting given your upgrade path: Confluence 10.0 introduced an upgrade to Apache Tomcat 10.1 and migrated from javax.servlet to the jakarta.servlet namespace, which means any custom server.xml connectors or proxy configurations may need to be reviewed for compatibility. If your reverse proxy config wasn't updated as part of the upgrade, it could be causing the upload response to fail silently. If none of that surfaces the issue, the best next step is to raise a support ticket with Atlassian and ask them to check whether there is a known regression in 10.2.0 specifically for this flow.

Hope this helps!

https://support.atlassian.com/confluence/kb/upload-attachment-function-does-not-work-in-editing-mode/

https://confluence.atlassian.com/doc/confluence-10-0-upgrade-notes-1612579096.html