Thunderbolt bridge connection problem

Hello everyone!

I can't find a solution to my problem:

I have an iMac (2012) and a MacBook Pro retina (2014) and I want to connect them with a Thunderbolt cable to share files.

When i connect the cable to both macs I get a bridged connection only on the MBP and no sign of it on the iMac.

If I disconnect the cable from the iMac side, I get on the MBP, disconnected.

I also have a Thunderbolt-Ethernet adapter for the MBR and if I connect the macs thought ethernet it works fine.

Also if I set the MBP to disk mode (cmd+t) at startup the iMac is able to see the disk.

The cable is new, bought yesterday from an Apple Store.

I tried to reboot both systems and to reset the p-ram on both without change.

Do you you any clues and suggestion?

Thank you!

Tomas.