Hello ! I have a jazz 2 version 1.20 and I want to know what levels on the site (jazz2online) are compatible with this version, I tried a few but I give error or do not detect them, maybe you tell me about who I am and be single player ways.

1.20 is an outdated version of JJ2. The game developers distributed a free official 1.23 patch that you can get on Jazz2Online here. This patch is completely legal to download and use on your game so there is no reason not to do it.

Jazz2Online downloads section offers information about level version on every individual download page. This version may be one of: 1.23, 1.23+, TSF, TSF+. If the version is TSF (The Secret Files, 1.24), the level was almost certainly made in a new version of JCS. This version is not backward compatible, so TSF levels cannot be played in any older versions of the game. TSF is an official expansion pack and it is not technically legal to download it if you don't own it. If the version includes a "+" sign, the level probably makes use of JJ2+ features. JJ2+ is an unofficial mod of the game that may be installed on 1.23 and TSF. If you're not using JJ2+, the levels may be possible to play to some degree but will likely not work correctly.

Most levels labelled as 1.23 will be playable in 1.20, but without the 1.23 patch you may occasionally experience bugs or errors that render a level unbeatable. Jazz2Online does not keep track of which levels are compatible with older versions such as 1.20 so you would have to find out on your own.

Originally Posted by Sir Ementaler

Most levels labelled as 1.23 will be playable in 1.20, but without the 1.23 patch you may occasionally experience bugs or errors that render a level unbeatable.

As far as my vague memory goes, 1.21 - 1.23 levels won't load in 1.20 in the same manner as TSF levels won't load in 1.23. In online play, 1.20 can't join with any other version than it's own, as well as non-1.20 players not being able to join your 1.20 servers. Of course levels saved with 1.20 are perfectly compatible with 1.21 - 1.23 and TSF. Aside from curiosity there's no good reason to use 1.20 as you're pretty much isolated and missing the Trigger Zone event.

1.20 was the version originally released by Project2 in EU/AUS while 1.21 was released on disc by GODGames in the US.

1.21 was never released as a patch as far as I know. 1.22 was a Jazz2.exe-overwrite patch, while 1.23 actually came as an installer-like patch that conveniently patched whatever you had installed as long as it wasn't one of the OEM versions.