http://mugenshare.com/uploads/f8cf3f370ca.bmp

How I got this:
I compiled my map in the PTI like always (hold ctrl). Since I only need Hammer for decompiling to BSP (because of the map <mapname> command) I did so, like with all of my chambers taken from the PTI.

The problem is now, that Hammer stops decompiling and doesn't go any further because of the last error that it shows. Normally, yellow marked messages are no problem and ignored / fixed automatically.

As far as I can read of this, somewhere is a model (old_speaker_big.mdl) placed outside of the main map. I want to delete it so that the error is just gone. But how to I find it without searching an eternity for it?

If this is a Stylemod map it'll be part of the entry/exit doors. Collapse the doorframe instance and delete the speaker (not the actual entrance/exit corridor.