I also have several customer sites that stopped working.
All of them with a lower serial number that you provide a fix for. It might legaly correct to only publish such a bug fix for those versions of Sitefinity. But from a moral point of view this is really low level support, not worthy of the once so great Telerik support.
I mean I paid for a valid, perpetual license that should stil be good. Now I'm left with either the choice to reverese engineer your code and try to come up with a fix myself, or using some other .NET version redirect hack.
I'm sorry, but the help you give here is of no use for many of us. If at least the Framework Article would point out the faulty DLL or the .NET DLLs that cause the trouble, this would already help a bit.