Operating system and graphics card
Short description of error
Open an old File with activated Clamp - Sampling: It open it without new Direct/Indirect Clamp activated, thus resulting in other Render Result than previous Version.
I suggest to set Clamp Direct/Indirect both to Clamp Value saved in .Blend file.
Exact steps for others to reproduce the error
Based on a (as simple as possible) attached .blend file with minimum amount of steps