This error means that the Salesforce Call Center component required by the Salesforce CTI adapter and the CTI adapter on your PC do not match. These are usually installed as part of the Flexor installation but may become out of sync due to updates in the CTI adapter provided by Salesforce.
Please check the version of the adapter installed on your PC and the Call Center installed in Salesforce match (both version 3 for instance). If they do not (e.g. after an update in Flexor), check that you have also updated the Call Center XML in Salesforce as per the installation instructions here.
It is possible to have multiple Call Centers installed in Salesforce to allow gradual migration of users, by editing the Call Center "Internal Name" so that each one is different.