Non-7-bit ASCII character(s) in line &1 (see long text)

What causes this issue?

The source code contains (at least one) non-7-bit ASCII character in
line &V1&. These characters can cause problems in the customer system
(in combination with the system code page).
The error occurred when the the following template was edited: &V2& &V3&
&V4&.

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?

Only use 7-bit ASCII characters, even in comments.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.