When adding a camera to the VMS it is possible to select a list of more than one set of credentials. In this case the vcore VMS will try and communicate with the camera with each of these credentials in turn until it gets a positive response. However this process can trigger a security feature on some Avigilon cameras which lock out the user account for a period of time after several incorrect password attempts. 

This will typically show up in the device logs from the camera itself;

"currently locked out due to too many failed authentication attempts""

The solution to this is to wait until the lock-out period expires, and try again selecting only the correct credential from the list of credentials. Further details on the functionality of the lock-out can be found in the camera documentation.