Trouble joining shared notebooks

[Slawrenc 0]

I have students joining Evernote and creating notebooks where they take notes and do assignments. The notebook is then shared with me so I can view their work. I have 104 students who have joined. Once I hit that number I haven't been able to join any other notebooks. The students set up the account, share the notebook, I open the email but every time I click on the "Open Shared Notebook" it responds with "failed to join notebook". Any ideas? Thanks.