You cannot process contact persons

What causes this issue?

You cannot assign contact persons to vendors. As a result, you cannot
carry out the following functions:

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

maintaining contact persons for a vendor
using contact persons in partner functions for a vendor
copying contact persons by batch input

System Response

How to fix this error?

Error message extract from SAP system. Copyright SAP SE.