Function &1 limited/not available for 'SAPGUI for HTML' -> &2

What causes this issue?

The function, &V1& , was called from The Business Workplace or Internet
(www) Browser, but the browser doesn't support this functionality.
Function &V1& was changed by the system to &V2& (if this value is set,
then no error message appears, and the function continues).

System Response

An error message is produced if the requested function cannot be
accessed. Examples for this can be (status: March 2000):
Specified download/upload functionality cannot be used. SAP plans to
provide a Basis solution for file up-/downloads that will make it
unnecessary to change ABAP coding by application development.
SAP shortcuts will not be supported by SAP GUI for HTML.
SAP Frontend Printing will not be supported by the SAP GUI for HTML.
The SAP GUI for HTML will not support multiple parallel SAP GUIs for the
Windows environment. Applications that open new windows by program will
currently fail. SAP is trying to implement a better system behavior for
that, so that at least opening sessions will stay active.
....
Normally, it is not necessary for the application to produce an error
message caused in the "SAP transaction classification", but sometimes
only a partial function is affected.
An information or success message appears if the program changed the
flow caused in the active 'caller' (web browser). Examples for this can
be:
Convert ALV GRID control output to ALV classic output
....
Other restrictions:
Accelerator keys, for example: F1, F4, TAB, and ENTER, have been
pre-defined by the browser vendor. Therefore, they cannot be used in the
SAP GUI for HTML.

How to fix this error?

Dependent on the type of message, the system handles the problem
automatically, or the requested function cannot be used within this
environment, <ZH>or</>
Use a different GUI (Java or Win)

Procedure for System Administrators

To get additional information within the SAP online service system or
SAPNet, please search for keywords, for example: "Transaction
classification", "HTML-GUI", "Workplace", "Web-Browser", "ITS Internet
Transaction Server",... or a combination of those search terms.

Error message extract from SAP system. Copyright SAP SE.