I ran into a problem when trying to upgrade from 10.11 to latest.
Unable to find a version of 'Castle.Core' that is compatible with 'EPiServer.CMS.Core 10.10.5 constraint: Castle.Core (>= 3.3.3 && < 4.0.0)'.
My current version is
That problem occurs, because the latest UI package also requires you to upgrade CMS.Core to the 11.x version. CMS.Core 11.x has support for newer Castle.Core packages. So upgrade all EPI packages to the 11.x version range.
How do you upgrade the package? If you in Visual Studio select one specific package source and not All for example, the dependencies which are located on a different package source are not upgraded and this typically causes this behavior.
I tried as you suggested to upgrade only Core then the package Amesto.AutoConnect.EPiServer10 revealed that its most likely the problem. So i uninstalled Amesto.AutoConnect.EPiServer10 and installed Amesto.AutoConnect.EPiServer11 then i could run Update-Package EPiServer.CMS.UI
Thanks for the input