I tried several things, with and without Telerik, Framework 3.5 and 4.0. The flood is the same, but the current situation (FW 3.5 and Telerik) seems to be slower than before. Now you can see, that you have to wait until the list with script blocks clears-up, before the next function acts.
Thanks for the support. We will going to use Telerik in our solutions.