Hi adkrev,
If I understand correctly, avast is warning you that there is an infection in your system restore. As I see it the problem is the possible infection, not the warning. Setting avast! to ignore the file would be like closing your eyes to the real problem.
If you suspect this is a false positive then download a nonresident scanner like Bitdefender (free edition) or ClamWin and use that for a second opinion. Or, do an on line scan like TrendMicro Housecall.
If you think this is true infection, then turn off system restore. This will delete your restore points and viruses hiding in them. Reboot, and run another scan. If your are receiving no alerts at this point turn system on again.