When using the "drop" mode of invalid recipients Symantec Messaging Gateway (SMG) 10.6.2 frequently logs error level messages indicating that it was unable to parse the invalid recipients header.
2012-06-18T11:18:25-07:00 (ERROR:22374.2741410704):  Unexpected data found when parsing Invalid Recipient header: 1rbush, 2012-06-18T11:20:43-07:00 (ERROR:22374.2867288976):  Unexpected data found when parsing Invalid Recipient header: rcpt_test,
An attempt to parse portions of the X-Invalid-Recipients header failed due to a known issue. The X-Invalid-Recipients header is generated temporarily while the email message is being processed by the engine but does not exist in the final, delivered copy of the message.
This message is no longer logged in SMG 10.6.3.
For earlier versions, this error can be safely ignored. The message is processed and delivered properly in spite of this error.