1. Click on the 'Start' button at the bottom of the desktop to open the Start menu.
2. Move to the 'Run' option in the Start menu. Click on 'Run' to open the Run text box.

3. Type 'regedit' in the Run text box and hit the enter key to open the Registry Editor.
4. Navigate to the top of the tree menu on the left side of the screen. Click the ' ' sign next to 'HKEY_LOCAL_MACHINE. Continue clicking the plus signs next to 'SOFTWARE,' 'Microsoft,' Microsoft Games,' 'Flight Simulator' and '9.0.' Each time you click to open a folder (plus sign) a new list of folder will become available. Move to the next section and click the plus sign again.
5. Select the 'EXE Path' from the pane on the right side of the window and right click on your mouse. EXE Path sits inside the final folder opened in the last step, '9.0.'
6. Choose Modify from the options that appear next to the cursor.
7. Move to the 'Value Data' text box and delete the information in the box. Move to the end of the data and press the backspace button on your keyboard until all information is gone. Click 'OK' to continue.
8. Close the registry editor.
9. Open the Microsoft support page for this error in your computer browser (see 'References').
10. Download the file in step 3 of the 'Update Error Type: 25'on the page to your computer desktop. Click on the file and then the 'Download' button. Close the computer browser once download is complete.
11. Locate file 'Fs91upd.exe' on the desktop. Double-click on the file to begin installation. Follow the onscreen instructions to complete the repair.