I had the same issue - try to import the powershell module for CM: "Import-Module 'C:\Program Files (x86)\Microsoft Configuration Manager\AdminConsole\bin\ConfigurationManager.psd1'"
Hi, I have been struggling with the same issue recently. Microsoft recommends (and that's how we got it working) to have a global group in the user's forest and add the user to that group. In the resource forest, create a Domain Local group and add the user's group to it. The group MUST BE domain local! Try it out and let me know if it works or not. P.S.: In theory, it should work also if you create a domain local group and add the user directly - however, it's not recommended.