If you get the following error when calling a SAP BAPI via a web service from .NET:
CX_SY_CONVERSION_NO_DATE_TIME:XSLT exception.An error occurred when deserializing in the simple transformation program /1BCDWB/WSS2B813A2D0E86D9A4A67.Value 22/12/2009 1:00:00 PM is not a valid date in accord with the XML format for ABAP
Then the date type may not have been inferred correctly if you are using the .NET XSD.exe tool (e.g. if the field has a default in an SAP BAPI, it may not be able to infer the correct date type and just treats the date as a string.).
To fix this problem you can simply do a date conversion to the correct format (e.g. via the DateTime.ToString("yyyy-MM-dd"). The format it is expecting in ABAP is yyyy-MM-dd e.g. 2009-12-30.