Could not load file or assembly 'Microsoft.ReportViewer.WebForms'
This link gave me a clue that I didn't install a required update (my problemed concerned version nr, v11.0.0.0)
ReportViewer 2012 Update 'Gotcha' to be aware of
I installed the update SQLServer2008R2SP2
I downloaded ReportViewer.msi, which required to have installed Microsoft® System CLR Types for Microsoft® SQL Server® 2012 (look halfway down the page for installer)
In the GAC was now available WebForms v11.0.0.0 (C:\Windows\assembly\Microsoft.ReportViewer.WebForms v11.0.0.0 as well as Microsoft.ReportViewer.Common v11.0.0.0)
I've installed Microsoft.ReportViewer.2012.Runtime nuget package and problem has been solved without installing ReportViewer.msi or sql feature pack 12
You need to reference both Microsoft.ReportViewer.WebForms and Microsoft.ReportViewer.Common and set the CopyLocal property to true. This will result in the dll's being copied to our bin directory (both are necessary).