The base class includes the field ‘reportViewer’, but its type (Microsoft.Reporting.WebForms.ReportViewer) is not compatible with the type of control (Microsoft.Reporting.WebForms.ReportViewer)

This error is generated after update related in some way with reports of Microsoft SQL Server Reporting Services, or their parts.

To remedy sufficient to modify the existing applications web.config. This is a key value or a reference to the library – Microsoft.ReportViewer.WebForms, which may be in some versions such as version = 9.0.0.0, 8.0.0.0, and so on.

To re-operation reports is a need to return to the previous value. For example, from version 9.0.0.0 to version 8.0.0.0 etc.