I had the same issue last year, Link worked from the accountant side but not the client.  I had to contact Profile as it was a background setting they had to change.  No issues this year.

I talked to Profile support, they do recognize it is a backend issue. Still waiting to get this resolved.

Hi, thank you for using Intuit ProFile Community

Have the user click on the sign out link. They will then be directed to sign in again, ( I had the same screen pop up and it worked for me).

Please call us if that does not work because an agent should be able to help. You can reach an agent at 1-800-452-9970

I apologize for the inconvenience but hope this helps  

I tried with the Profile support, there is no solution so far. Did not get any exact answer why it is not working. Never had issue with Intuit LINK since its inception.  Probably this year I had to find alternative solutions for my clients!!!

Hi, thank you for using Intuit ProFile Community

Product development has resolved the issue with the client log in window for link. You should expect a resolution on a call or chat with support. Please contact support 1-800-452-9970 or use messaging through ProFile help menu.

I apologize for the inconvenience but hope this helps