Symptoms
When you try to save your changes for EDI Agreement that use the EDIFACT/X12 encoding protocol settings, the changes are not saved. Additionally, you receive the following error message:
Unable to cast of type 'Microsoft.BizTalk.Administration.EdiExt.ComboItem' to type 'System.String'
Resolution
The fix that resolves this issue is included in the following update for BizTalk Server:
Cumulative Update 5 for BizTalk Server 2016
Status
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
References
Learn about service pack and cumulative update list for BizTalk Server.
Learn about BizTalk Server hotfixes and cumulative update support.