invalid XML error cause due to virus effect, corruption, or PST damage. These reasons harms your outlook pages and thus you find inaccessibility and invalid xml errors. Hence to fix these error and to prevent further issues and risks, one must fix immediately Outlook XML file files and folders from the navigation pane setting. But in case you fails to do so, then must use Outlook Repair Tool to fix those. If you have Outlook 2007 version of MS outlook, then can prefer to outlook 2007 Repair tool for that.
Go to "Control Panel" > "Programs" > "Programs and Features."
Find Microsoft Office in the list of installed programs.
Right-click on Microsoft Office and select "Change."
Choose the "Repair" option and follow the prompts to repair the Outlook installation.
Run Outlook in Safe Mode:
Press the Windows key + R to open the "Run" dialog.
Type outlook.exe /safe and press Enter to start Outlook in safe mode.
If Outlook opens successfully in safe mode, the issue may be caused by an add-in or extension. Disable add-ins one by one to identify the problematic one.