General ⇒ [Fix] LaTeX Error: Unknown message 'caption-code-by-class-deactivated' (tocbasic / KOMA-Script)

[gwadasly]

Hi everyone,

I recently updated MiKTeX (December 2025) and encountered a breaking error when compiling my thesis. I managed to fix it and wanted to share the solution here to help others.

**The Error:**
! LaTeX Error: Unknown message 'caption-code-by-class-deactivated' for module (LaTeX) 'tocbasic'.

**The Cause:**
It seems to be a bug in the latest version of `tocbasic.sty` (v3.49). The package tries to use an error message before it is actually defined in the file.

**The Solution (Workaround):**
You need to manually edit the file `tocbasic.sty` in your LaTeX distribution folder (e.g., `.../tex/latex/koma-script/tocbasic.sty`).

1. Open `tocbasic.sty`.
2. Search for the block starting with:
\msg_new:nnnn { tocbasic } { caption-code-by-class-deactivated }

ex :
\msg_new:nnnn { tocbasic } { caption-code-by-class-deactivated }
{
Loading~of~class-dependent~code~for~package~caption3~prevented\MessageBreak
line~context.
}
{
The~caption3~package~attempts~to~detect~classes~known~to~it\MessageBreak
using~a~number~of~heuristics~and,~if~necessary,\MessageBreak
reload~class-dependent~code.\MessageBreak
Unfortunately,~the~code~from~caption-koma.sto,~for~example,\MessageBreak
is~no~longer~compatible~with~the~KOMA-Script~package~tocbasic\MessageBreak
since~KOMA-Script~3.46.\MessageBreak
Therefore,~the~tocbasic~package~attempts~to~prevent~these~files\MessageBreak
from~being~loaded~by~pretending~to~caption3~that~a~standard~class\MessageBreak
is~being~used.\MessageBreak
Since~the~caption3~package,~as~part~of~the~caption~collection,\MessageBreak
is~no~longer~maintained,~and~since~the~KOMA-Script~author~himself\MessageBreak
is~trying~to~maintain~the~compatibility~of~the~caption~package\MessageBreak
with~KOMA-Script,~this~is~currently~the~best~known~method\MessageBreak
to~prevent~unnecessary~warnings~from~caption~or~caption3.
}

(It is located near the end of the file).
3. Cut (Ctrl+X) this entire definition block.
4. Paste (Ctrl+V) it at the beginning of the file, just after the `\ExplSyntaxOn` command.
ex :

\if@tocbasic@old@latex@found\else
\ExplSyntaxOn

% --- PASTE HERE---
\msg_new:nnnn { tocbasic } { caption-code-by-class-deactivated }
{ ... }
{ ... }
% -------------------------------------------

\bool_new:N \g__tocbasic_patch_all_bool

This ensures the message is defined before `tocbasic` tries to trigger it.

Hope this helps!

[Stefan Kottwitz]

Hi gwadasly,

welcome to the forum!

Thanks for letting us know! It's indeed helpful to post your fix here in the forum, as people may find it later when googling for such a fix, so thanks for that.

Stefan

[joezhou]

Thanks for your share. This solves my problem.