Error after upgrading v9.31 to v10 : type or namespace name 'ESRI' could not be found

[Vincent_ZFan]

Hello,

I am upgrading ArcGIS customization for ArcCatalog 9.31 from VS2008 project to VS2010 ArcCatalog v10.0 project.

VS2010 conversion results shows successfully converted.

I added the new reference to the reference and  changed the reference property "Specific Version" to False.
Rebuild the project.

I got many errors like below (more in screenshot)[ATTACH=CONFIG]17171[/ATTACH]

Error 4 Error 4 The type or namespace name 'ESRI' could not be found (are you missing a using directive or an assembly reference?)

I have tried to remove the reference and added them back.
This does not fixed it either.

I also tried to upgrade on another box. Same errors.

Any idea?

Thanks.

[RichardWatson]

When there are multiple errors building a project in Visual Studio, it can be confusing.  I say that because one error can cause other errors.  Suggest that you go to the Output window and focus on the first error which occurs.

[NeilClemmons]

Make sure your target platform is set to the 3.5 .NET Framework.  VS2010 defaults to the 4.0 .NET Framework when you create new projects, which is not supported by the ESRI SDK at ArcGIS 10.

[Vincent_ZFan]

Neil, the project did target .net framework 3.5.
Thanks guys for the inputs!