Hello there!
It looks to me like you are trying to use a control that requires registration in the web.config file (ie, the Office/Charts/Extended controls).
1.) Please make sure your project References Gizmox.WebGUI.Common, and also Gizmox.WebGUI.Forms.Office, Gizmox.WebGUI.Forms.Extended, Gizmox.WebGUI.Forms.Charts. (It probably does, but just make sure. Try removing Gizmox references and add the Gizmox references again)
2.) Add these to your web.config file:
<WebGUI>
<Controls>
<Control Type="Gizmox.WebGUI.Forms.*, Gizmox.WebGUI.Forms.Office, Version=1.0.0.0, Culture=neutral, PublicKeyToken=d50c2c7452ba77d9" />
<Control Type="Gizmox.WebGUI.Forms.*, Gizmox.WebGUI.Forms.Extended, Version=1.0.0.0, Culture=neutral, PublicKeyToken=d50c2c7452ba77d9" />
<Control Type="Gizmox.WebGUI.Forms.*, Gizmox.WebGUI.Forms.Charts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=d50c2c7452ba77d9" />
</Controls>
</WebGUI>
I hope this helps!!
Ryan