Hi Telerik Team!
This is FYI.
I am running VS 2008 SP1. I had the Q1 2009 Rad controls installed on my C: drive (the Complete version). I uninstalled. I installed the Q2 2009 Rad controls on my D: drive without the 2.0 assemblies. I ran into installation errors.
Eventually, I gave up and went back to installing the Q2 2009 Rad controls on my C: drive (I don’t think I was given a custom option so the complete package must have been installed). However, I kept getting the Invalid FORMATETC Structure error when trying to drag and drop NET35 controls. I tried different things suggested on the web but to no avail.
One other symptom is that when I moused over the controls in the ToolBox list, not all of them would show version information. I could drag and drop NET20 controls but not NET35 controls.
Finally, I uninstalled again. Then I went through the registry and manually deleted most of the Telerik entries. I also searched my hard drive and deleted any Telerik files I found.
I installed again. This time I was given the custom option for the C: drive. I installed without the 2.0 assemblies. I tried my IDE but I still got the Invalid FORMATETC structure error.
Then I found an item on the web that said I should reset the IDE toolbox. So I did this. Prior to this, I still had two lists in the toolbox (one for NET35 controls and one for NET20 controls) even though I chose to install only the 3.5 assemblies. Anyway, after I reset the toolbox (which took a few minutes), the list for the NET20 controls disappeared and I was able to drag and drop NET35 controls.
I hope you find this information helpful.