The 9.3 types used to be in ESRI.ArcGIS.ADF have been split into ESRI.ArcGIS.ADF.Local (base classes) and ESRI.ArcGIS.ADF.Core (utility functions) at 9.4 beta2. [...]
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The 9.3 types used to be in ESRI.ArcGIS.ADF have been split into ESRI.ArcGIS.ADF.Local (base classes) and ESRI.ArcGIS.ADF.Core (utility functions) at 9.4 beta2.
Also at beta2, ESRI.ArcGIS.ADF is marked as deprecated so you should reference ESRI.ArcGIS.ADF.Local in any new/upgraded project instead when inheriting these .NET base classes. Existing 9.x projects referencing ESRI.ArcGIS.ADF should still compile but it is recommended to move to the .Local assembly instead when upgrading.
See Changes to the ESRI.ArcGIS.ADF assembly in http://help.esri.com/en/sdk/9.4/ArcObjects_NET/ConceptualHelp/index.htm#/d/0001000002M2000000/
Hope this help.