Hi Abi Rami,
I know you might have tried some of these steps already, but give it a shot through these steps.
1. First, in the plugin registration tool, select the plugin step and you will see 'start profiling' button. Click on it.
2. While it is profiling, perform the action that you want to debug. You will receive a profile file which you need to download and save it somewhere.
3. Stop profiling.
4. In visual studio, build your plugin.
5. In plugin registration tool, hit 'debug', you will see a wizard where in you need to select the profile you downloaded and the assembly that you built in the 4th step and keep it aside(do not close).
6. In Visual studio, you need to place a breakpoint wherever you want and then click 'Debug' in the menu options.
7. Select 'Attach to Process' and select 'Plugin registration tool' in the available processes section.
click ok.
8. In the wizard(Replay Plug-in Execution) which you did in 5th step, hit 'Start Execution'.
Your breakpoint in the plugin will be hit for you to debug.
Try these steps and I am sure it will work.
Thank you.