Should I quit if I'm having problems with the Marie Curie industry partner? Unfortunately I am having a really hard time with the industry partners that have made me think I should quit. First of all, they are aggressive every time I come up with a research idea, and they shut it down in an aggressive way. I have been having some issues to be there to the secondments (bureaucracy not from my side). It is now on their side how to solve the bureaucracy. They have been trying to convince me the secondments are not important, and I can work for them from abroad. They are not being transparent or providing information about what they are doing to have me in place and finally one of them just got out of control and insane and scream at me in a meeting in front of everyone. Frankly I don't want to work with these people again.

What should I do in case of having troubles with the industry partner? What are the risks for the project, if I quit?
I would not quit a MCS fellowship. Either you solve the problem with the industry partner, maybe by collaborating with another person or unit (if possible), or try to minimize as much as possible their importance in your project. Usually secondments are a nice addition but a MCS project should stand on its own even without the secondment.

You could also try to reach out to someone in the Horizon2020 and see if they have a person that can help with this kind of problem. In the meantime I would also gather some proofs that you can use to build your case. In the worst case you will have to justify to H2020/EU why the secondment was not useful/successful.

PS: how to improve the working relationship with industry partner seems more a question for another Stack.