Line command '&' contains invalid characters; correct these characters

What causes this issue?

The line command contains invalid characters.

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?

With the line command RESET, you can delete the current and marked line
command.
To display the allowed line commands, place the cursor on the line
number and press the help key.

Error message extract from SAP system. Copyright SAP SE.