Error CMP500: Inserted <buffer name> buffer(s) on the net <your net> for local clock legalization.

Clock and PLL cores cannot be assigned to regions. If a net assigned to a local or quadrant clock region drives a clock or PLL core, Compile needs to insert a buffer to guarantee that the cores driven by that net can be assigned to the local or quadrant clock region. The clock and PLL cores can then be placed on any legal position..

Action

None. The message appears to alert you to the fact that a buffer has been inserted.