"No screen/popup processed in current SAP GUI mode.": I'm developing a script that uses GuiXT Controls and I get the error message:
No screen/popup processed in current SAP GUI mode. -> Synactive Q&A Controls Nr. 023
What causes this error and how can I avoid it?
The error occurs if a GuiXT Controls function such as Controls, WebView, CallJS is executed immediately after a new SAP GUI mode has been opened, before processing a screen or, in some cases, a popup screen. We are working on a general solution. In the meantime we suggest you use the following workaround:

Situation 1
You use the GuiXT Controls functions, e.g. a VBScript call, in an InputScript that you start with /O...:

Pushbutton .... /Oxxxx process="myinputscript.txt"

// myinputscript.txt
Screen abc
  CallVBS ...

Workaround:
Start the InputScript with another screen command that calls up the same transaction:

// myinputscript.txt
Screen abc
  Enter "/Nxxxx"

Screen abc
  CallVBS ...

Situation 2
You use the GuiXT Controls function in a transaction that starts with a popup screen (e.g. XD01).

Workaround:
Start your GuiXT script with

if V[_transactionid=XD01.1]
  Enter "/Nxd01" -visible
  Stop Script
endif
....

i.e. if transaction XD01 is called up the first time in this SAP GUI mode, you call it again. With "Stop Script" you suppress the further processing of the script.

For popup screens within a transaction,  use a flag variable

if not V[popup_processed=1]
  Set  V[popup_processed]  1
  Enter "?" -visible
  Stop Script
endif

With GuiXT version 2024 Q3 1 and above the best solution is the following:

if Q[firstPopup]
  Enter "?" -visible
  Stop Script
endif

This automatically covers any previous popups in the current mode.