A key point to understand when you're installing Adobe Digital Publishing Suite tools is that there are two separate installers for InDesign CS5/CS5.5. It's also important to understand why there are two separate installers. It's necessary that the Folio Builder panel stays in sync with the Folio Producer web client. If changes the web client require an update to the Folio Builder panel, you are prompted to update the Folio Builder panel when you open it. However, it's not always necessary to update the Folio Producer tools as well.
In some instances, it's necessary to update the Folio Builder panel without updating Folio Producer tools. For example, if you created a custom viewer using an older set of tools, updating your tools and editing folios results in an error. Customers receive a "Please update your app" error message when they open the new folios in the old viewer. Or, you could be getting ready to publish a folio, and updating the tools before you publish can cause an unnecessary disruption.
Starting with v21, you can target the viewer version when you create a folio InDesign CS5 or later. You can specify only a v20 viewer version or later. To target an older viewer version, such as v18, install an older set of Folio Producer tools in InDesign CS5/CS5.5.
For InDesign CS6, there is only one installer for the DPS tools. Choose Help > Updates and install the DPS Desktop tools. You can then target the viewer version (v20 or later) when you create a folio. You can edit the version in the Folio Properties dialog box. However, you can select only a more recent version. You cannot specify an older version. Instead, create a folio.