'ReportViewer' is ambiguous in the namespace 'Microsoft.Reporting.Webforms'

I am using assembly Microsoft.ReportViewer.Webforms Version=10.0.0.0. However, each time I build the solution it adds Microsoft.ReportViewer.Webforms Version = 8.0.0.0 by itself. I tried removing Version 8.0.0.0 reference manually and tried building it again but it keeps adding the later version.
Any help would be appreciated.
Thanks
 
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