MSE flags activation cracks. Avast doesn't.
There are other issues peculiar to a given install which can occasionally occur with either MSE or Avast so I just change to the other one in that case.
Switch to Avast 5.
If your Windows 7 is that slow, you may need to troubleshoot it and your hardware or get a better reinstall: Win7 Troubleshooting fundamentals re-install windows 7
Hope you have a better day.