Errors while upgrading to 1.90

I've been trying to set up 1.90 on a web hosting package with EUKHOST. 1.80 works fine on it but I can't get 1.90 working. I've so far had to remove a couple of lines from the web.config to get it to get anywhere. Now, I get this:

"Could not load file or assembly 'AjaxControlToolkit' or one of its dependencies. This assembly is built by a runtime newer than the currently loaded runtime and cannot be loaded."

It's getting frustrating.

https://www.nopcommerce.com/boards/t/5286/runtime-newer-than-the-currently-loaded-runtime-and-cannot-be-loaded.aspx
or this link

Andrei, the thread you linked to shows that others have the problem, but there was no solution.

The solution is there: "...As soon as it was set to run .NET 4.0 integrated mode it worked."