Hi Björn, It seems like an error with the site root path. How are you performing the upgrade? Where is the site installed? Is this error specific to one site? Which version of cms 4 are you trying to upgrade ?Possible workaround could be to use the offline package to upgrade your site.
I have the exact same problem when trying to upgrade from 4.61 to 4.62. It's driving me nuts :-)Problem is that I have no idea where to start and would appreciate any help I could get.Could it be something with Unified filesystem? I think I've read something about that earlier.