The function '&' is not available

What causes this issue?

You tried to call the additional function pool using the function that
appeared in the message. This function is no longer available under
this name.
This function has either been renamed or deactivated.

System Response

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

How to fix this error?

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.