getting CSRF Invalid and booted out from my forum can someone help with how to fix errorbug?

Thanks for the report! A "CSRF Invalid" error combined with being logged out usually means your session got cleared server-side while you still had a page open. The security token in that page then no longer matches, and you appear logged out.
A few questions to narrow it down:

• What version of Flatboard are you running, and are any plugins active?
• Does this happen after leaving a tab open for a while (idle), or right away when submitting a form?
• Do you have multiple tabs/windows of the forum open at once?
• Did you recently change your own password or your account's group/permissions?
• Is your forum behind a reverse proxy or CDN (Cloudflare, etc.)?
  In the meantime, could you check stockage/logs on your server for entries like:
• CSRF validation failed
• Session expired
• Session migrated
  around the time this happens? That'll tell us exactly which mechanism is triggering it.
  Workaround (for now): Fully reload the page before submitting a form if you've had it open for a while. That refreshes the CSRF token and should avoid the error.