InvalidOperationException from HbmJoinedSubclass in NHibernate 3 on Mono 2.8

I'm trying to run my app on Mono and I'm getting the following error. It used to run fine on Windows/.NET 4. All I've changed is the config to use MySQL instead of SQL Server.

Any ideas what is going on here?

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Server Error in '/' Application

To be XML serializable, types which inherit from IEnumerable must have
an implementation of
Add(NHibernate.Cfg.MappingSchema.HbmJoinedSubclass) at all levels of
their inheritance hierarchy.
System.Collections.Generic.IEnumerable`1[[NHibernate.Cfg.MappingSchema.HbmJoinedSubclass,
NHibernate, Version=3.0.0.1002, Culture=neutral,
PublicKeyToken=aa95f207798dfdb4]] does not implement
Add(NHibernate.Cfg.MappingSchema.HbmJoinedSubclass).

Description: HTTP 500. Error processing request.

Stack Trace:

System.InvalidOperationException: To be XML serializable, types which
inherit from IEnumerable must have an implementation of
Add(NHibernate.Cfg.MappingSchema.HbmJoinedSubclass) at all levels开发者_运维百科 of
their inheritance hierarchy.
System.Collections.Generic.IEnumerable`1[[NHibernate.Cfg.MappingSchema.HbmJoinedSubclass,
NHibernate, Version=3.0.0.1002, Culture=neutral,
PublicKeyToken=aa95f207798dfdb4]] does not implement
Add(NHibernate.Cfg.MappingSchema.HbmJoinedSubclass).
 at System.Xml.Serialization.TypeData.get_ListItemType () [0x00230]
in /private/tmp/monobuild/build/BUILD/mono-2.8.2/mcs/class/System.XML/
System.Xml.Serialization/TypeData.cs:366
 at System.Xml.Serialization.TypeData.get_ListItemTypeData ()
[0x00016] in /private/tmp/monobuild/build/BUILD/mono-2.8.2/mcs/class/
System.XML/System.Xml.Serialization/TypeData.cs:298
 at System.Xml.Serialization.TypeData..ctor (System.Type type,
System.String elementName, Boolean isPrimitive,
System.Xml.Serialization.TypeData mappedType,
System.Xml.Schema.XmlSchemaPatternFacet facet) [0x00104] in /private/
tmp/monobuild/build/BUILD/mono-2.8.2/mcs/class/System.XML/
System.Xml.Serialization/TypeData.cs:94
 at System.Xml.Serialization.TypeData..ctor (System.Type type,
System.String elementName, Boolean isPrimitive) [0x00000] in <filename
unknown>:0
 at System.Xml.Serialization.TypeTranslator.GetTypeData (System.Type
runtimeType, System.String xmlDataType) [0x00241] in /private/tmp/
monobuild/build/BUILD/mono-2.8.2/mcs/class/System.XML/
System.Xml.Serialization/TypeTranslator.cs:243
 at System.Xml.Serialization.TypeTranslator.GetTypeData (System.Type
type) [0x00000] in /private/tmp/monobuild/build/BUILD/mono-2.8.2/mcs/
class/System.XML/System.Xml.Serialization/TypeTranslator.cs:163
 at
System.Xml.Serialization.XmlReflectionImporter.GetReflectionMembers
(System.Type type) [0x00244] in /private/tmp/monobuild/build/BUILD/
mono-2.8.2/mcs/class/System.XML/System.Xml.Serialization/
XmlReflectionImporter.cs:774
 at System.Xml.Serialization.XmlReflectionImporter.ImportClassMapping
(System.Xml.Serialization.TypeData typeData,
System.Xml.Serialization.XmlRootAttribute root, System.String
defaultNamespace) [0x0007a] in /private/tmp/monobuild/build/BUILD/
mono-2.8.2/mcs/class/System.XML/System.Xml.Serialization/
XmlReflectionImporter.cs:343
 at System.Xml.Serialization.XmlReflectionImporter.ImportTypeMapping
(System.Xml.Serialization.TypeData typeData,
System.Xml.Serialization.XmlRootAttribute root, System.String
defaultNamespace) [0x0006e] in /private/tmp/monobuild/build/BUILD/
mono-2.8.2/mcs/class/System.XML/System.Xml.Serialization/
XmlReflectionImporter.cs:217
Version information: Mono Runtime Version: 2.8.2 (tarball Tue Jan 4
15:08:58 MST 2011); ASP.NET Version: 4.0.30319.1

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Upgrading to the latest version of NHibernate 3 fixed by problem. I was running on an old alpha release of 3.0... doh!