Hi. Big trouble here. I wanted to test the backup of my Iphone and stg went awfully wrong. First I copied all apps using SSH and win scp : /private/var/stash/Applications.VtOLXz on my PC ; Before doing that, following the tutorial, I set properties on 755. I did a test and erased one of the app (av player), no problem, and copied again. Since, not only the app is not back but I can-t access Cydia anymore!! But the rest of the third party apps still function. Anyone could help? Thanks ahead.

Cydia is probably broken because you set all the properties of /Applications to 755. I don't know who told you to do that, but it's not a good plan. Cydia.app/Cydia_ must have properties 6755 (the 6 is important).

The other application doesn't work because you have not set its properties to 755. These properties (permissions) don't survive a stay on a Windows system, so you must change them after putting the files back (doing it before the backup makes no sense).