You added those DLL files:
c:\Windows\assembly\GAC_MSIL\CrystalDecisions.Web\12.0.2000.0__692fbea5521e1304\CrystalDecisions.Web.dll
c:\Windows\assembly\GAC\CrystalDecisions.Web\12.0.1100.0__692fbea5521e1304\CrystalDecisions.Web.dll
to your project.
The
CrystalDecisions.Web.CrystalReportViewer
class exists in both files.
You can try to remove one of them from your project (don't delete one of them from your hard disk!).