AACC 6.3.210
CCMM Administrations\ Web Comm\ Config\ Concurrent Chat Session is set to 1
Setting the Concurrent sessions to '1' means that a Customer contact can only establish a single Chat session.
Customer contact is determined by the email address entered in the Chat request template.
If a Chat session connection should fail after the initial Chat session is queued, any additional chats will fail. The Error message at Customer Chat indicates that the "You have exceeded your maximum number of concurrent connections"