&1 contains invalid characters

What causes this issue?

At least one invalid character is used in the tag.

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?

Some characters are not supported in tags. Invalid characters are :, ;,
., ?, &, [, ], (, ), #, ^, *, @, !.
Avoid using invalid characters.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.