Several errors for ESRI.ArcGIS.ADF classes in ArcObjects10.5.1

[AmitaNarote]

Getting an error - 'BaseCommand' is ambiguous in the namespace 'ESRI.ArcGIS.ADF.BaseClasses' when a custom toolbar in ArcGIS Desktop 10.1 is migrated to 10.5.1

Not only this but I am getting same error for following - 

1. 'MxCommandBars' is ambiguous in the namespace 'ESRI.ArcGIS.ADF.CATIDs'

2. 'MxCommands' is ambiguous in the namespace 'ESRI.ArcGIS.ADF.CATIDs'

3. 'MxDockableWindows' is ambiguous in the namespace 'ESRI.ArcGIS.ADF.CATIDs'

Like all errors are for 'ESRI.ArcGIS.ADF', But I am unable to find any help for ArcObjects 10.5.1 on ESRI support / GeoNet.

Please help.

Amita.