When installing Avast! Antivirus software, you can either try the software and install a demo version that is good for 60 days or activate the software license. If you order a full version of the software, a license file downloaded along with the software. To use the license, you must specify the location of the license file to the License Manager when prompted during installation. Including the license file will also stop any warnings and pop-ups, and allow updates for the software.
Right-click on the Avast! icon in the bottom of the system tray.
Select "About Avast!" from the menu that opens.
Choose "License" in the screen that opens.
Click the "Browse" button. Locate the license file on the computer in the browser window. The license is named "license.dat." The exact location will differ for each user, but you are likely to find it in the Windows temporary folder.
Click the "My Computer" folder in XP, or "Computer" folder in Vista and 7, in the desktop "Start" menu.
Click "Local Disk (C:)" folder.
Select "Windows," and then click the "Temp" folder. The installation file should be located in there.
As an alternative, you can also enter in ".dat" in to the search field at the bottom of the "Start" menu. Click the "Search" icon and all .dat files will be listed in the results. Click on the "See more results" option, if necessary. A window will open with all of the .dat files and their exact location. Find the "installation.dat" file that belongs to the Avast! software and note its exact location. Then go back to the Avast! browser window and try inserting the file again by clicking through the file folders according to the file location you noted.