Beno,
What you've done is written two sessions on your disc, but you've erased the file entries for the first session from the index.
The first session is still there, but not connected to the disc index any more. Earlier versions of ECDC would let you import the lost session, but current versions won't

so the old recovery methods don't work.
Instead, go to www.isobuster.com and download IsoBuster 2.4 - it's a free download. Install and run it.
When you run it, IsoBuster will ask you for your registration details. Just click on the
'Free Funct. Only' button on the bottom right.
With your disc in the drive, IsoBuster should show you something like this. . . .
Click to view attachmentSee, it shows Session 1 with a track, and session 2 with another track. It will most likely be showing you the contents of your last session, the one you can see in Windows.
Click on the + to the left of the session 1 disc, and then click on the + to the left of track 1, and then click on either the blue or red disc label under track 1. You should now see the contents of the first session - the one you want.
Highlight the files in that session [Ctrl-A] and go up to the top toolbar File > Selected Objects > Extract Objects. Select a destination, and click OK. The files from your missing first session will be recovered to your destination,
free.Your original disc has an "orphaned" session on it which you can't recover on disc, so after you have all the files from both sessions copied onto the hard drive write them to a fresh disc and throw the old one away. Just remember that when you "Load Disc" for a multisession disc in the future, all you're loading is the earlier INDEX not the files, and you don't delete files from it. [I don't think you'll forget that after this

]
HTH,
Brendon