Here is a link to the list of changes in the latest version (Q1 SP1) . There you can also track the changes we made in previous releases:
When upgrading RadControls version please make sure that your project references telerik dlls from with equal version numbers. You may also use the Project Update utility
that automates this step for you.
Note that keeping our tools nearly 100% compatible with previous versions is a top priority for us. However due to the great complexity and variety of features RadControls offer and the huge API we support, in some cases it is not possible to avoid breaking changes. We provide a list with such changes, if there are any, for each release.
Let us know if the problems persist.
the Telerik team