Server is unwilling to process the request - Active Directory - Add User via C#

I had a similar issue where I was trying to add a member to a group. Specifically trying to add a group to a group and getting the same helpful error 'The server is unwilling to process the request' The answer provided by the OP did not work for me.

For me, the reason I was unable to add a group to my group was because the group I was trying to add members to was a 'global' scoped group whereas it needed to be a 'universal' scoped group. Hope this helps someone.

This question took me a lot of time to solve. First of all, the error message looks like a joke. Second, there is nothing more, just that message.

Anyway, I managed to fix it by:

1. Making sure that userDn contains the whole path (e.g., "LDAP://server-address/CN=" + userDn + ",OU=optional,DC=your-domain,DC=com". This is actually very important, if you don't supply the full path it will throw an Exception from HRESULT: 0x80005000.

2. Replacing dirEntry.Properties["member"].Add(userDn); by entry.Invoke("Add", new object[] { userDn });

Then I wanted to remove a user and I expected entry.Invoke("Remove", new object[] { userDn }); to work. However, this devilish AD will only work if you use lower case "remove", so entry.Invoke("remove", new object[] { userDn }); worked for me.