Error Code Portal
MicrosoftWindows WinINetError code

12155

ERROR_HTTP_HEADER_ALREADY_EXISTS

Alternative forms: 0x00002F7B · 0x2F7B · ERROR_HTTP_HEADER_ALREADY_EXISTS

What does this code mean?

Code 12155 · An issue reported by Windows WinINet.

Official explanation · Original text

The header could not be added because it already exists.

Troubleshooting and diagnostic links

First check that the document's product, version, and environment match your situation.

This entry links only to official code reference documentation. No separate troubleshooting procedure has been verified.

Source and terms of use

Error Messages (Wininet.h) ↗

Creator: Microsoft and MicrosoftDocs contributors
License: Creative Commons Attribution 4.0 International
Checked on: 2026-11-12

Modifications: Extracted numeric codes, symbolic names and English message text; converted Markdown/HTML to plain text and normalized whitespace; added Korean product context, namespace labels, status classification and separately labeled official links. No machine translation of message text.

Source details · Original licenses and notices