silverlight - "The resource MultipleIdDefinition was not found" on deserialization on Windows Phone 7 -

i started getting windows phone 7 app. don't know changed in data deserialization have caused this. idea means?

system.runtime.serialization.serializationexception occurred   message=the resource multipleiddefinition not found in system.runtime.serialization   stacktrace:        @ system.runtime.serialization.referencedobjectcache.add(string id, object referencedobject)        @ system.runtime.serialization.xmlobjectserializerreadcontext.addnewobjectwithid(string id, object obj, boolean isreference)        @ system.runtime.serialization.xmlobjectserializerreadcontext.addnewobject(object obj, boolean isreference)        @ system.runtime.serialization.xmlformatreader.invokebeforedeserialization(classdatacontract classcontract, xmlobjectserializerreadcontext context)        @ system.runtime.serialization.xmlformatreader.initializecallstack(datacontract clcontract, xmlreaderdelegator xmlreaderdelegator, xmlobjectserializerreadcontext xmlobjcontext, xmldictionarystring[] membernamescoll, xmldictionarystring[] membernamespacescoll)        @ system.runtime.serialization.classdatacontract.readxmlvalue(xmlreaderdelegator xmlreader, xmlobjectserializerreadcontext context)        @ system.runtime.serialization.xmlobjectserializerreadcontext.readdatacontractvalue(datacontract datacontract, xmlreaderdelegator reader)        @ system.runtime.serialization.xmlobjectserializerreadcontext.internaldeserialize(xmlreaderdelegator reader, string name, string ns, datacontract& datacontract)        @ system.runtime.serialization.xmlobjectserializerreadcontext.internaldeserialize(xmlreaderdelegator xmlreader, int32 id, runtimetypehandle declaredtypehandle, string name, string ns)        @ system.runtime.serialization.xmlformatreader.internaldeserialize(object value, type type, string name, string ns, xmlobjectserializerreadcontext context, xmlreaderdelegator xmlreader)        @ system.runtime.serialization.xmlformatreader.readvalue(type type, string name, string ns, xmlobjectserializerreadcontext context, xmlreaderdelegator xmlreader)        @ system.runtime.serialization.xmlformatreader.readcollectionitem(collectiondatacontract collectioncontract, type itemtype, string itemname, string itemns, xmlobjectserializerreadcontext context, xmlreaderdelegator xmlreader)        @ system.runtime.serialization.xmlformatreader.readcollectionitems(deserializedobject desobj, collectiondatacontract collectioncontract, int32 membersread, int32 size)        @ system.runtime.serialization.xmlformatreader.readcollection(deserializedobject desobj, collectiondatacontract collectioncontract, int32 membersread)        @ system.runtime.serialization.xmlformatreader.deserialize(xmlobjectserializerreadcontext context)        @ system.runtime.serialization.xmlformatreader.initializecallstack(datacontract clcontract, xmlreaderdelegator xmlreaderdelegator, xmlobjectserializerreadcontext xmlobjcontext, xmldictionarystring[] membernamescoll, xmldictionarystring[] membernamespacescoll)        @ system.runtime.serialization.classdatacontract.readxmlvalue(xmlreaderdelegator xmlreader, xmlobjectserializerreadcontext context)        @ system.runtime.serialization.xmlobjectserializerreadcontext.readdatacontractvalue(datacontract datacontract, xmlreaderdelegator reader)        @ system.runtime.serialization.xmlobjectserializerreadcontext.internaldeserialize(xmlreaderdelegator reader, string name, string ns, datacontract& datacontract)        @ system.runtime.serialization.xmlobjectserializerreadcontext.internaldeserialize(xmlreaderdelegator xmlreader, type declaredtype, datacontract datacontract, string name, string ns)        @ system.runtime.serialization.datacontractserializer.internalreadobject(xmlreaderdelegator xmlreader, boolean verifyobjectname)        @ system.runtime.serialization.xmlobjectserializer.readobjecthandleexceptions(xmlreaderdelegator reader, boolean verifyobjectname)        @ system.runtime.serialization.xmlobjectserializer.readobject(xmldictionaryreader reader)        @ ...        @ microsoft.phone.shell.phoneapplicationservice.firelaunching()        @ microsoft.phone.execution.nativeeminterop.fireonlaunching() 

if you're not knowlingly deserializing xml, can guess either:

• the app's isolated storage contains app-state xml (e.g. appsettings)
• or there's problem configuration xml app

to try fix this, could:

1. take in properties folder of project - xml configuration files there ok? if open them in editor, there warnings or errors shown?
2. uninstall app emulator and/or phone (you can try restarting emulator or factory resetting phone)

if not, post more info , we'll try more - interesting problem!