When I repair permissions, get one reading that can't be repaired. "Warning: SUID file "System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS/ARDAgent" has been modified and will not be repaired." What does this mean?

When I repair permissions in disk untilities, I get one result that cannot be repaired:

Warning: SUID file "System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/MacOS/ARDAg ent" has been modified and will not be repaired.

I recently had a new hard drive installed by Apple, after mine failed. The permissions seem to get out of whack quite often, and I get the message above.

Can you please tell me what may be going on?