Cognizant — Unable to register in one cognizant portal

I tried to follow the steps mentioned in email but I was unable to continue Step-1 : when clicked on the link it is showing "You are currently signed in as [protected]@outlook.com, however, [protected]@gmail.com was invited. Do you want to switch to [protected]@gmail.com?"
then I clicked on switch account, it showing:
"Invitation redemption failed
An error has occurred. Please retry again shortly".
I have tried from different PC's and mobilesbutnoluck