From the beginning of February, Sagepay will no longer support browsers or systems that support SSL v3. It is no longer considered safe to use SSL v3.
In practice, this means vendors or shoppers using Windows XP or IE8 and earlier will no longer be able to use Sagepay because they will not be accepted at SagePay's secure pages. You should advise any affected users to upgrade their platform, or use an alternative browser such as Firefox or Chrome.
Note that there is nothing in Kartris relating to the SSL type used; these issues are solely down to the server and browser.
SagePay has also announced that it will stop supporting protocol 2.23 and earlier later this year. The Kartris SagePay plugins have been compatible with protocol 3.00 for several years now; you can download the latest Kartris version and pull the required SagePay DLLs from there if you are unsure that you have the latest. Ensure too that you update the payment gateway's settings to use protocol 3.00. We advise doing this and running tests to ensure you're using the newer protocol well before the 2.23 cut off date.
For any further information, please contact SagePay's support.