It appears that our script at http://www.e-junkie.com/ecom/o_plug.php is returning errors for any transactions set to call it, this script is called to handle PDF stamping and a variety of other functions. This is resulting in an error message going out on any transaction that uses that script.
Any orders related to these transactions are still processing otherwise, but without the stamping feature or any other special settings that depend on the script.
We're working on fixing this ASAP and will update here when it is done.