Hi, 

Recently we have been getting random errors when users is accessing the Approver page which has been edited using Nintex forms. The error logs is showing the following.

Failed to retrieve form from workflow. Error: There was an error deserializing the object of type Nintex.Forms.Form. Character reference not valid. Line 1, position 302.. Stack trace:
at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.XmlObjectSerializer.ReadObject(XmlDictionaryReader reader)
at Nintex.Forms.NfUtilities.DeserializeObjectWithDataContractSerializer(String xml, Type type)
at Nintex.Forms.NfUtilities.DeserializeObject(String xml, SerializationType method, Type type)
at Nintex.Forms.FormsHelper.XmlToObject(String formMarkup)
at Nintex.Forms.SharePoint.Helper.GetFormWithLicenseCheck(String formMarkup, Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.GetForm(String formKey, FormData formData, Boolean hasEnterpriseLicense)

Failed to handle form host page on initialize event. Error: There was an error deserializing the object of type Nintex.Forms.Form. Character reference not valid. Line 1, position 302.. Stack trace:
at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.XmlObjectSerializer.ReadObject(XmlDictionaryReader reader)
at Nintex.Forms.NfUtilities.DeserializeObjectWithDataContractSerializer(String xml, Type type)
at Nintex.Forms.NfUtilities.DeserializeObject(String xml, SerializationType method, Type type)
at Nintex.Forms.FormsHelper.XmlToObject(String formMarkup)
at Nintex.Forms.SharePoint.Helper.GetFormWithLicenseCheck(String formMarkup, Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.GetForm(String formKey, FormData formData, Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.ConfigureFiller(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.InitialiseForm(Boolean hasEnterpriseLicense)
at Nintex.Workflow.Forms.ControlTemplates.TaskForm.OnInit(EventArgs e)

System.Xml.XmlException: Character reference not valid. Line 1, position 302.
at System.Xml.XmlExceptionHelper.ThrowXmlException(XmlDictionaryReader reader, String res, String arg1, String arg2, String arg3)
at System.Xml.XmlBufferReader.GetCharEntity(Int32 offset, Int32 length)
at System.Xml.XmlUTF8TextReader.ReadCharRef()
at System.Xml.XmlUTF8TextReader.ReadEscapedText()
at System.Xml.XmlUTF8TextReader.Read()
at System.Xml.XmlDictionaryReader.ReadContentAsString(Int32 maxStringContentLength)
at System.Xml.XmlBaseReader.ReadElementContentAsString()
at ReadCalculationFormControlPropertiesFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryStringr] , XmlDictionaryStringr] )
at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserializeWithSurrogate(XmlReaderDelegator xmlReader, Type declaredType, DataContract surrogateDataContract, String name, String ns)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
at ReadArrayOfFormControlPropertiesFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryString , XmlDictionaryString , CollectionDataContract )
at System.Runtime.Serialization.CollectionDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserializeWithSurrogate(XmlReaderDelegator xmlReader, Type declaredType, DataContract surrogateDataContract, String name, String ns)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Int32 declaredTypeID, RuntimeTypeHandle declaredTypeHandle, String name, String ns)
at ReadFormFromXml(XmlReaderDelegator , XmlObjectSerializerReadContext , XmlDictionaryStringr] , XmlDictionaryStringr] )
at System.Runtime.Serialization.ClassDataContract.ReadXmlValue(XmlReaderDelegator xmlReader, XmlObjectSerializerReadContext context)
at System.Runtime.Serialization.XmlObjectSerializerReadContext.InternalDeserialize(XmlReaderDelegator reader, String name, String ns, Type declaredType, DataContract& dataContract)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserializeWithSurrogate(XmlReaderDelegator xmlReader, Type declaredType, DataContract surrogateDataContract, String name, String ns)
at System.Runtime.Serialization.XmlObjectSerializerReadContextComplex.InternalDeserialize(XmlReaderDelegator xmlReader, Type declaredType, DataContract dataContract, String name, String ns)
at System.Runtime.Serialization.DataContractSerializer.InternalReadObject(XmlReaderDelegator xmlReader, Boolean verifyObjectName, DataContractResolver dataContractResolver)
at System.Runtime.Serialization.XmlObjectSerializer.ReadObjectHandleExceptions(XmlReaderDelegator reader, Boolean verifyObjectName, DataContractResolver dataContractResolver)

We have tried to open the form and there is no error opening and saving the form. We are not sure if it is data on the form that is causing the error or it is some configuration issue as this is something which happen randomly.