Until you have made customizations to a DarqUI component, no configuration file will exist for it in the \POI subfolder. This is not an error, but the ui.log file will indicate a failure to load data from these non-existent files. In the utility go to the bottom of the Manage page and click "Generate files." Generating empty configuration files is harmless and will eliminate the extraneous log file messages that pertain to DarqUI.
The lines about inventory upgrade are from windows that no longer exist in the default UI. There are references to them in the default and the developers have never removed them. Again not an actual error, and the game simply steps over the references. Same with the examine_ misspelling. That exists in the default game for every player, but the XML engine is robust enough to step over the missing file reference.
Data outside of container tags means there are extra blank lines in one or more of the XML files. Again, not an error that will do any harm to the game. I have meticulously kept blank lines out of the DarqUI files where possible, to reduce the number of log file lines that alarm players, but the default UI and other custom UIs have plenty of blank lines that fill the log with the messages.