When I try to use the webdatechooser control on a webform, I receive a "Failed to load ViewState" error when posting back. If I remove the control the problem goes away. Any ideas?

I am not doing any dynamic content, I am literally just including the control on a form and it breaks.

Versions:

.Net 3.5

<add assembly="Infragistics35.WebUI.WebDateChooser.v9.1, Version=9.1.20091.2087, Culture=neutral, PublicKeyToken=7DD5C3163F2CD0CB"/>

<add assembly="Infragistics35.WebUI.Shared.v9.1, Version=9.1.20091.2087, Culture=neutral, PublicKeyToken=7DD5C3163F2CD0CB"/> 

Exact error:

Failed to load viewstate.  The control tree into which viewstate is being loaded must match the control tree that was used to save viewstate during the previous request.  For example, when adding controls dynamically, the controls added during a post-back must match the type and position of the controls added during the initial request.