E_FAIL error...DLL is looking to wrong directory

Hi all,
Been banging my head against the monitor on this for a while.  Hoping you can help.
I have a class calling a DLL, which references another class.  The code currently works in production, but I'm trying to move the code to a new server, and I get the dreaded E_FAIL error.  (Very helpful)
I can see in the stack trace, however, that the DLL seems to be looking for my class in the wrong directory:
[COMException (0x80004005): Error HRESULT E_FAIL has been returned from a call to a COM component.] ABCDE.OMI.XYZ.DoTheThing(String PSID) in C:\DevServer\WrongPath\TheThingHelper.cs:67 utils.theThing(String username, String psid, String& msg) in e:\NewServer\CorrectPath\App_Code\utils.cs:218 In the example above, I can see the call to "DoTheThing(string PSID)" is looking to the same path as on ...