1. Go to the Installshield Web page (see Resources) and download the appropriate fix. Find out the version number of the IsScript engine by right-clicking on the file you are attempting to install and select 'Properties.' Click the 'Version' tab in the dialog and look at the 'Version' section. Download the appropriate fix according to the file version.
2. Click 'Save' in the dialog box and double-click the installation file to install the fix and eliminate the 'Setup Is Unable To Find or Update ISScript.msi' error.

3. Go to the 'C:\Windows\Installer' folder in Explorer and right-click 'Installer' and choose the 'Properties' option. Click the tab entitled 'Security' and make sure the 'System' and 'Administrator' accounts have full permission on the folder. This will ensure that you have permission in the 'Installer' directory.
4. Click the desktop's 'Start' button and click the 'Run' icon. Open the Microsoft registry editor by typing 'regedit' into the 'Run' text box and clicking the 'OK' button. Go to the left-side pane of the editor and double-click the 'HKEY_LOCAL_MACHINE' folder, then double-click 'SOFTWARE.' Go to the 'InstallShield' folder and right-click it. Select the 'Permissions' option and add the 'System' and 'Administrator' accounts by clicking the 'Add' button. Click 'OK' in the dialog.
5. Ensure that all active programs are closed and run Installshield.