Symptoms

Attachment can't be retrieved or inserted into a page.  The following warning message appears on the page:

Diagnosis

This issue is not affected by a custom layout or velocity changes as per the following KBs:

• Macro browser, Tree View, Insert Image and Preview are broken in Confluence 3.1.1
• Error Loading Macro Browser, Tree View, Insert Image, Page Restrictions and Preview in Confluence 3.2 or Later

Cause

Reverse proxy is configured with http compression (gzip).

Resolution

Remove/disable gzip completely.