Why does the Web browser on Nokia 9300(i)/9500 devices give an error message when I try to open it?

The reason might be a corrupted web browser bookmark file.

Go to the File manager  \System\Apps\Opera -folder. Delete Bookmarks file (or replace with a working one).The Web browser will create new empty bookmarks file when it is started.If bookmarks file is locked, you can turn off Web browser by closing it with Ctrl+Shift+Chr+k.