Hi Jacob,
I noticed that in the Product information field you have indicated RadTabStrip for ASP.Net, however, I am sorry to inform you that we no longer provide support for the classic controls. Please read more on the matter
here.
As a side note we have not experienced such problems. In case you are using any custom skins or styles that you apply to RadTabSrip control or some other controls that hold the RadTabStrip, you could try to disable these styles/skins and check if the RadTabStrip appears on the page.
All the best,
Kate
the Telerik team
Consider using RadControls for ASP.NET AJAX (built on top of the ASP.NET AJAX framework) as a replacement for the Telerik ASP.NET Classic controls, See the product support lifecycle here.