I'm using the FirstData Gateway from this thread: https://www.nopcommerce.com/boards/t/1968/first-data-global-gateway.aspx?p=1
It installs properly and works up to the point of order confirmation, at which point I get an error stating "Unable to load DLL 'lpssl.dll': The specified module could not be found. (Exception from HRESULT: 0x8007007E)". That seems to be a specific dll for this solution, and the file is in the bin directory of the store.
I'm running on a windows 2008 (64-bit) server, if that makes any difference.