It may be a client-side button ID conflict.

I still haven't got around to customising the button range for TCLights, however there shouldn't be any buttons drawn except when the menu is open (unless you have the HUD enabled).

It's possible that Lazy is trying to update the lights status text of a button which TCLights has deleted (ie when closing the menu)?

• If you have the TCLights HUD on, try turning it off.
  
• If TCLights HUD is off, does it still happen if you haven't opened a TCLights menu since last starting Lazy & LFS?

Edit: Looks like I was ninja'd. May still be useful for others to troubleshoot though.