The type or namespace name 'SharePoint' does not exist in the namespace 'Microsoft'

Problem:
The type or namespace name 'SharePoint' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)   
C:\mohant\Perforce\dev\solutions\sharepoint\SecureSharePoint\SPObjectHelper.cs    7    17    RSASecureSharePointLibrary

Solution:
The reference it is looking for is missing. Make sure the program is installed or if it is available add the reference.
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\ISAPI\Microsoft.SharePoint.dll