The online documentation is always for the latest official release. You're using an older version of Telerik Reporting where does assemblies do not exist and you should use the documentation embeded in Visual Studio or download the chm file for this version.
As for the original problem, close all Visual Studio instances but one and choose Reset Toolbox
from the context menu of Visual Studio Toolbox. If this does not help, please run Telerik Reporting installer from command prompt
with logging information enabled:
msiexec /i path_to\Telerik_Reporting_QX_2011_DEV.msi -l*xv install.log
and attach the log file to a support ticket with information about your problem.
the Telerik team
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