Very hard to add members to a project

Very hard to add members to a project

I have been using zoho for a few months to keep track of my freelance projects. I'm happy with it as a unique user, but I have a project I'm collaborating with 4 other people and I decided to include them in Zoho. Here are my problems:
- I added 4 members, and it only accepted 2, even though I received the confirmation email that the invitation was sent to all of them.
Of the two people accepted, one had a very hard time to login, he had to register three times with my help until it finally got in, but I created a notebook that crashes his computer every time he opens it.
So far my collaboration experience has been a bumpy road.

Has anybody experienced the same issues?