A problem with AVG virus scanner
I often recommend the free AVG anti-virus program as an alternative to a fee-based program. Most of the time it works as well as any other. But according to this article, AVG may wrongly identify an important computer file as harmful. You may see a warning message like this.
AVG advises you to delete the file, but this will prevent your computer from booting correctly. AVG has posted instructions for recovering your system here. You can find other remedies on this web page.