Sets the error message for the field specified. If there's already a message stored for this field, it's overwritten unless append is set to true, which appends the message to the existing error using a semi-colon as separator. The message stored is returned by IDataErrorInfo[fieldName];

void SetEntityFieldError(
	string fieldName,
	string errorMessage,
	bool append
)

Sub SetEntityFieldError ( 
	fieldName As String,
	errorMessage As String,
	append As Boolean
)