Hello,
Please use ESRI.ArcGIS.AxControls assembly if you are using the Engine controls; use ESRI.ArcGIS.ADF Assembly to replace the utilities assembly. Details please refer to the links:
How to migrate ArcGIS 9.3 Desktop and Engine stand-alone applications to ArcGIS 10
http://help.arcgis.com/en/sdk/10.0/arcobjects_net/conceptualhelp/index.html#/How_to_migrate_ArcGIS_9...
ESRI.ArcGIS.ADF Assembly
http://help.arcgis.com/en/sdk/10.0/arcobjects_net/componenthelp/index.html#/Overview/000200002pnn000...
Regards,
Chelsea