Snom have made some changes to how their newer phones can be connected to via their CSTA interface.
To resolve this please update to Flexor build 2.1.154 or above.
First un-install the existing version of Flexor via Microsoft Windows, Programs and Features. Flexor settings will be retained as they are stored in the Microsoft Registry even after un-installing.
If you are running newer versions of Windows, if after running the Flexor installer, a message appears saying Windows protected your PC, click on "More Info" and then click on "Run Anyway".
Once installed, Flexor should connect to your Snom as normal. If you are still experiencing difficulties please contact support.