Hi folks,

I have a .NET managed add-in for Excel which is throwing the following error
when I make a call to Application.CheckOut("my-url-here"):

System.Runtime.InteropServices.COMException (0x800A03EC): Exception from
HRESULT: 0x800A03EC

A few details: it is running in the main thread and the URL is correct. The
same code works just fine as a VB macro. I've played around with the Trust
Center with futility.

I've been struggling with this for some time now.

If anyone has any ideas, it would be much appreciated. Thanks.