System error: Invalid callup of method/form "&1"

What causes this issue?

A system error occurred.
The order of the form calls or method calls is not permitted.

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?

Contact the relevant SAP consultant or the Hotline. Include the first
10 pages of your shortdump in your message.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.