Calling COM method results in 'type mismatch' error code -2146828275

I'm calling a COM object from .NET, and the 4th line below is erroring out.

object1 = CreateObject("something1.something2")
object1.OpenDocument(fileNameCopy, False, 0)
object1.SetProperty("Status", "Edit")
object1.CloseDocument()

The error is:

Type mismatch

Error code:

-2146828275

How can I be passing the wrong type to CloseDocument()? Is it something other than a method? If so, how can I determine how to use it if I only have the DLL, and not the source code?

This works on other machines, so it seems to be an environment or version issue.

I searched on SO and found similar questions, but no solution.