Here is probably the answer:

Open your map file in a text editor and look at the line. Look at previous lines for understanding the syntax of the map file. If there is nothing visible, maybe it's an invalid non visible character. Depending of your text editor, you can look at the line in hexadecimal mode, or saving it in another character format...

There's no line nº 4592.. could any experienced mapper help me out?

P.S. :

Teo opened it, compiled it and played it with no difficulties. Could it be the editor?

Try GtkRadiant

GTK owns man. I couldn't even get Quark to work and the GUI didn't appeal to me much anyhow.

It'll take me a while to get used to those complicated editors...

For your corrupted file Fido, just open the map file with GtkRadiant. If it works, re-save it and it would probably solve the problem. There is also a "Plugins|bobtoolsz|Brush Cleanup" feature that could be useful sometime...

After that you may be able to open the map file again with Quark.

Personally I don't like the user interface of Quark, but I agree that when you are accommodated to a tool, it's generally a pain to change.

Had some problems sorted out, here's my map so far:

It looks so cool! I can't wait it to be released!

Hot damn! Nice stuff there! Reminds me of a level, can't remember which one though.

It's set on a creepy underground bunker in Stroggos, with weak lighting and few ammo and health. Most of it is destroyed by bombings, so the player will have to manage it through ventilation shafts, sewage and more.