Being working on Salesforce Integration project about a year. Even now and then Few Surprises come along.
The SOAP end point which is used for integration was working fine until they decided to add support for TimeZone. Not sure how they are managing dates at server but now in all date fields in SOAP request required to be sent logged in users timezone.
Earlier life was easy and all needed to be sent in, is Date (Not Timestamp). So a simple MM.dd.yyyy formatted date was sufficient for SOAP request to succeed. However now as TimeZone came into picture the expected format is changed to ‘MM.dd.yyyy HH:mm:ss Z’.