The limitation doesn’t apply to distiguished fields.


Thanks to another blogger, I didn’t waste a lot of time on this, and as he points out, it’s documented.  Still, it’s one of those things that can trip you up.  The error you get is:



There was a failure executing the receive pipeline: “Microsoft.Biztalk.DefaultPipelines.XMLReceive”. Source: “XML Disassembler” Receive Location: “C:\ReceiveLocation” The property ‘propertyname’ has a value with length greater than 256 characters


According to the help,


ms-help://BTS_2004/SDK/htm/ebiz_sdk_editor_props_simn.htm



    Property field promotion is subject to the following limitations:



      • Promoting a string value that is longer than 256 characters in length may cause overflow exceptions at run-time

If you try to assign a string >256 characters in the midst of an orchestration, you get this, instead:



Uncaught exception terminated service Project.Orchestration(GUID1), instance GUID2


The value assigned to property ‘http://namespace:propertyname’ is not valid: ‘longstring‘.
       
Exception type: InvalidPropertyValueException
Source: Microsoft.XLANGs.BizTalk.Engine
Target Site: Microsoft.BizTalk.Agent.Interop.IBTMessage PrepareMessage(Microsoft.XLANGs.BaseTypes.XLANGMessage, System.Collections.IList, System.Collections.IList)


Help Link:
Additional error information:


The property ‘propertyname’ has a value with length greater than 256 characters.
       
Exception type: COMException
Source:
Target Site: Void Promote(System.String, System.String, System.Object)