Symptoms
An HTTP 400-Bad Request error pops up when trying to view a Smartform inside the context of a SharePoint site.
Diagnoses
This seems to be due to the size of the Auth cookie that is created for users that are utilizing the Smartform in any way. A browser cache clear did not do the trick.
Resolution
The registry settings near the bottom (in the More Information section) of the following Microsoft KB seem to resolve the problem when users are using 4.6.10:
https://support.microsoft.com/en-us/kb/2020943
If you are experiencing this type of error on 4.6.9 when utilizing Smartforms in any way, please log a support ticket, as there is a fix available.