ERROR: The type or namespace name 'ApplicationRegistry' does not exist in the namespace 'Microsoft.Office.Server' (are you missing an assembly reference)

I was working with BDC object model and accessing BDC application definition file from my custom ASPX page, I have included correct assembly for 'ApplicationRegistry' class but still it was giving me above error, after sometime I have realized that actually it’s looking for different assembly name to be included into page.

i.e. Microsoft.SharePoint.Portal (in microsoft.sharepoint.portal.dll).

After adding Microsoft.SharePoint.Portal assembly into page, I didn’t get any error :)

 Good Job!