Which description of the cause is true?

Multiple users report that when they try to login to Cisco Unified Communications Extension Mobility Manager this error is retrieved?
"Error:-[26] ?Busy, please try again"
Which description of the cause is true?
A. The intracluster Multiple Login Behaviour is set to Multiple Logins Not Allowed.
B. the Validate IP Address parameter is set to false, so the IP is not found in the trust list.
C. The number of concurrent log in and logout requests is higher than the Maximum Concurrent Requests service parameter.
D. the Extension Mobility Cache size has been lowered to 1000 and no more logins are allowed beyond this number.