BriskBard, CEF4Delphi, WebView4Delphi, WebUI4Delphi and WebUI4CSharp

The PopupBrowser demo shows how to avoid the "System Error Code 5" problem when the browser needs to show a new popup window in OSR mode.

It creates a hidden form that is used in the TChromium.OnBeforePopup event but in your case you should create a hidden tab.

There's a CEF issue with the TChromium.OnBeforePopup event and new popup windows in OSR mode :
https://github.com/salvadordf/CEF4Delphi/issues/249
https://bitbucket.org/chromiumembedded/ ... n-osr-mode

My situation is simpler:
I do not create tabs from TChromium.OnBeforePopup event.
I create them as in TabbedBrowser2, only every frame has an OSR browser.
Which is also created dynamically with different context

Then the solution is much easier.

Check all TChromium events to see if if any VCL control is created, destroyed or modified inside them.
Sometimes the VCL code has a hidden "RecreateWnd" call inside some other harmless looking function that causes all this issues.

Move all code that modifies VCL controls outside TChromium or TCEFApplication events.

I use version: CEF4Delphi uses CEF 73.1.12 which includes Chromium 73.0.3683.75.

As soon as I change to and use TChromium.OnBeforeClose instead TChromium.OnClose

I receive error system 5

Found a mistake!

I created tabs with Tchromium before the cef had time to initialize

Sometimes managed to initialize sometimes not