This would indicate that no member of staff has a role of SENCo on the system. If, for example, your Headteacher/Deputy Head/Assistant Head is the SENCo, but they carry out these duties via their Headteacher/Deputy Head/Assistant Head contract, you can annotate this when uploading your census.
If a member of staff has a specific contract for the SENCo roles this should be added on the staff profile.
To do this please go to Admin > Personnel > Staff - find the member of staff required. Click onto the grey cog next to contract info and add a new contract with SENCo as the role.