Memon please check that you are the administrator or have the privillage to edit the file.

To do this right click the file goto properties>security. There check whether your user has the full right. If not, click on the advanced button n make your user the owner. After making your user the owner click ok then again ok. After that again goto the security tab... now you will be able to add your user all the rights... After doing so click ok.

Now you should again try to edit and save the file.