Error text:

A message sent to adapter “FILE” on send port “spGwCustomers_Caterpillar_EDI210” with URI “C:\Integrations\EDI1\Customers\xxxx\outbound\210\Test_210_%datetime_bts2000%.TXT” is suspended.
Error details: The system cannot find the file specified. (Exception from HRESULT: 0x80070002)

Solution

The file not found can refer to the map .dll. The error to me is quite misleading, because it implies the directory/filename path listed in the error is the problem.
This can happen to me when I don’t run the MSI (or other deploy process) for a map on one of the BizTalk servers (when you have multiple BizTalk servers in the same group).

It sure would be nice if the error would give the actual missing filename (i.e. the map .dll name).