Against my better judgement I tried to install the latest version i.e. 5.4.1 at ihostasp.net, where I rarely have install problems. I got the message a couple of steps into the install wizard:

Could not load file or assembly 'Telerik.Web.UI' or one of its dependencies. Strong name signature could not be verified.  The assembly may have been tampered with, or it was delay signed but not fully signed with the correct private key. (Exception from HRESULT: 0x80131045)

So it's back to an earlier version for me.

Guys, I'd rather have fewer, more stable and better tested releases.

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 This is not about our internal testing in this case you appear to have a .NET Trust issue.

Yyou need to find out what your hosting provider is running and then alter this web.config line appropriately:

    <!-- set code access security trust level - this is generally set in the machine.config
    <trust level="Medium" originUrl=".*" />
     -->

  If that doesn't work then delete the Telerk.Web.UI.dll from the /Bin folder and re-upload it.

there is a post in the Telerik forums regarding the same error with a different Telerik.dll:

http://www.telerik.com/community/forums/aspnet-ajax/combobox/rad-control-not-working.aspx