Once resolved few problems , I successfully upgrade from DNN 7.0.6 to DNN 7.1.1.
But, I sometimes have general exceptions on some pages : it's always a JSON deserialization exception which occurs in DNN Core code
Here is the exception:

AssemblyVersion: 7.1.1

PortalID: 0

PortalName: Extranet Arcep

UserID: 1

UserName: DiDNNHost

ActiveTabID: 199

ActiveTabName: -T- Formulaire de déclaration

RawURL: /extranetarcep/OpérateursCE/DéclarationL331/TFormulairededéclaration.aspx

AbsoluteURL: /ExtranetArcep/Default.aspx

AbsoluteURLReferrer: http://localhost/extranetarcep/Op%C3%A9rateursCE/D%C3%A9clarationL331/TFormulaireded%C3%A9claration.aspx

UserAgent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; Trident/4.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; InfoPath.3; .NET4.0C; .NET4.0E)

DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke

ExceptionGUID: 95f6087d-9365-449e-9c4c-8b33820583a4

InnerException: Une erreur s'est produite lors de la désérialisation de l'objet de type DotNetNuke.Web.UI.WebControls.DnnDropDownListState. Jeton '"' attendu, mais 'Å' a été trouvé.

FileName:

FileLineNumber: 0

FileColumnNumber: 0

Method: System.Xml.XmlExceptionHelper.ThrowXmlException

StackTrace:

Message: DotNetNuke.Services.Exceptions.PageLoadException: Une erreur s'est produite lors de la désérialisation de l'objet de type DotNetNuke.Web.UI.WebControls.DnnDropDownListState. Jeton '"' attendu, mais 'Å' a été trouvé. ---> System.Runtime.Serialization.SerializationException: Une erreur s'est produite lors de la désérialisation de l'objet de type DotNetNuke.Web.UI.WebControls.DnnDropDownListState. Jeton '"' attendu, mais 'Å' a été trouvé. ---> System.Xml.XmlException: Jeton '"' attendu, mais 'Å' a été trouvé. à System.Xml.XmlExceptionHelper.ThrowXmlException(XmlDictionaryReader reader, String res, String arg1, String arg2, String arg3) à System.Runtime.Serialization.Json.XmlJsonReader.SkipExpectedByteInBufferReader(Byte characterToSkip) à System.Runtime.Serialization.Json.XmlJsonReader.ReadQuotedText(Boolean moveToText) à System.Runtime.Serialization.Json.XmlJsonReader.Read() à System.Xml.XmlDictionaryReader.ReadContentAsString(Int32 maxStringContentLength) à System.Xml.XmlBaseReader.ReadContentAsString() à System.Xml.XmlBaseReader.ReadElementContentAsString() à ReadSerializableKeyValuePairOfstringstringFromJson(XmlReaderDelegator , XmlObjectSerializerReadContextComplexJson , XmlDictionaryString , XmlDictionaryString[] ) à System.Runtime.Serialization.Json.JsonClassDataContract.ReadJsonValueCore(XmlReaderDelegator jsonReader, XmlObjectSerializerReadContextComplexJson context) à System.Runtime.Serialization.Json.JsonDataContract.ReadJsonValue(XmlReaderDelegator jsonReader, XmlObjectSerializerReadContextComplexJson context) à System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract) à System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 id, RuntimeTypeHandle declaredTypeHandle, String name, String ns) à ReadDnnDropDownListStateFromJson(XmlReaderDelegator , XmlObjectSerializerReadContextComplexJson , XmlDictionaryString , XmlDictionaryString[] ) à System.Runtime.Serialization.Json.JsonClassDataContract.ReadJsonValueCore(XmlReaderDelegator jsonReader, XmlObjectSerializerReadContextComplexJson context) à System.Runtime.Serialization.Json.JsonDataContract.ReadJsonValue(XmlReaderDelegator jsonReader, XmlObjectSerializerReadContextComplexJson context) à System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract) à System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, DataContract dataContract, String name, String ns) à System.Runtime.Serialization.Json.DataContractJsonSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName) à System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver) --- Fin de la trace de la pile d'exception interne --- à System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver) à System.Runtime.Serialization.Json.DataContractJsonSerializer.ReadObject(XmlDictionaryReader reader) à DotNetNuke.Common.Utilities.Json.Deserialize[T](String json) à DotNetNuke.Web.UI.WebControls.DnnGenericHiddenField`1.SetTypedValue() à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Control.LoadChildViewStateByIndex(ArrayList childState) à System.Web.UI.Control.LoadViewStateRecursive(Object savedState) à System.Web.UI.Page.LoadAllState() à System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- Fin de la trace de la pile d'exception interne ---

Source:

Nom du serveur:VM-W7-64-DNN

Any Idea ? I spent two hours searching an idea, but failed to imagine what happens....