Now fixed: COMException on x64 platforms when automating Office clients via the Primary Interop Assembly (PIA)

I had the original posting early in the year, and having got another question on it I checked and the hotfix was released back in April to resolve this issue  This hotfix is for the OS and not Project.  It also resolves the problem for other Office applications such as Word – which has some big object.  So if you are running x64 Vista or Windows Server 2003 and want to access large objects this is for you.


On a computer that is running the 64-bit version of Windows Vista or the 64-bit version Windows Server 2003, no more than 1,024 methods can be present in one COM interface.
This limitation makes some applications that have more than 1,024 methods, such as Microsoft Project (WinProj.exe), unable to contain more methods.

Hotfix information

A hotfix is available to extend the maximum number of methods on a COM interface to 2,048.

Just to help the search engines – the original error was:

Error HRESULT E_FAIL has been returned from a call to a COM component. System.Collections.ListDictionaryInternal.