Error 1721 - There is a problem with this Windows Installer package.
Scenario
This can be caused by insufficient privileges or something that is present preventing the installation from running. It is therefore advisable to ensure that you have Local Admin. rights and that any Anti-Virus software is (temporarily) disabled.It can also be caused by a previous version of Compare or Protect left in the registry, even though it has been uninstalled.
Resolution
Please check the following registry location and delete any Compare or Protect keys:HKEY_CLASSES_ROOT\Installer\Products
1. Ensure you are logged in as the administrator.
2. Click Start, then Run.
3. Type regedit.
4. Click the + to the left of HKEY_CLASSES_ROOT.
5. Scroll down to Installer and click the + to the left of it.
6. Scroll down to Products and click the + to the left of it.
7. Now we will back up this key, so we can reverse any damage (if caused)
8. Right-click Products, then click Export. Call the file whatever you choose and save it in a convenient location, perhaps the Desktop. This file can be double-clicked and it will allow you to replace all deleted entries.
9. In the expanded Products folder, click the first key in the list. In the right-hand pane you will see a value called ProductName. If this first key is a WS product, it will either say <no name>, Compare, Workshare, etc. In other words, it will be obvious which are which. To clarify, <no name> will indicate a WS product as well.
10. If this key is one to be deleted, please right-click it and then delete, hit yes to confirm.
11. Follow down this list and repeat the process for each key and remember don't worry as we have backed up all these keys.
If there are no keys relating to Compare\Protect then delete the Workshare Professional key and re-run the installation.