Error connection to "Adobe Campaign Classic"

Hello All, 

In my company, I have 4 users who experience now this Windows(?) error message when they are trying to connect (federatedId):

"Script error : Line 2, Char : 9910. Unable to get property 66786of undefined or null reference. Code 0 

 URL: https://adobe-api.arkoselabs.com/cdn/fc/js(...)/standard/funcaptcha_api.js

Do you want to continue running this script Yes / NO"

They sometimes can connect by cliquing on yes several times, They sometimes can't. 

Do you have an idea ? Thanks !