Hi,

I've upgraded an old project from version 6.1.6 to 6.2.5 but I'm now getting the above error in several places. 

Any ideas on what could be causing this would be greatly appreciated as I've been stuck on it for hours!

Thanks

An example of part of the stack trace is below:

[MissingMethodException: Method not found: 'System.Collections.Generic.IEnumerable`1<Umbraco.Core.Models.IPublishedContent> Umbraco.Web.PublishedContentExtensions.Where(System.Collections.Generic.IEnumerable`1<Umbraco.Core.Models.IPublishedContent>, System.Func`2<Umbraco.Core.Models.IPublishedContent,Boolean>)'.]
   Our.Umbraco.PropertyEditorConverters.MultiNodeTreePickerPropertyEditorValueConverter.ConvertPropertyValue(Object value) +0
   Umbraco.Core.Models.PublishedContent.CompatConverter.ConvertDataToSource(PublishedPropertyType propertyType, Object source, Boolean preview) +31
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__0() +39
   System.Lazy`1.CreateValue() +411
   System.Lazy`1.LazyInitValue() +152
   System.Lazy`1.get_Value() +75
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.<.ctor>b__1() +20
   System.Lazy`1.CreateValue() +411
   System.Lazy`1.LazyInitValue() +152
   System.Lazy`1.get_Value() +75
   Umbraco.Web.PublishedCache.XmlPublishedCache.XmlPublishedProperty.get_Value() +9
   Umbraco.Web.PublishedPropertyExtension.GetValue(IPublishedContentProperty property, Boolean withDefaultValue, T defaultValue) +73
   Umbraco.Web.PublishedContentExtensions.GetPropertyValue(IPublishedContent content, String alias, Boolean recurse, Boolean withDefaultValue, T defaultValue) +82
   Umbraco.Web.PublishedContentExtensions.GetPropertyValue(IPublishedContent content, String alias) +59