Open the “Person” window, and check whether any Person has the given User Connection. (Search for the User ID). If available remove the connection and try Deleting the user.

I hope this would help..

In short, you don’t delete users in IFS. Just inactivate them, this will free up the license. 

There are other places besides persons which are linked with the users. It won’t be easy to delete, as all history linked with that account will become orphan. 

I have the same question, how do you delete a contact on an account.  I went to the person screen and the user id field is blank. 

Just to clarify, we are trying to delete contacts on a customer account. the primary contact is the account holder, secondary contacts are staff, and the staff is no longer with the office. i can see that there is hide button and a block button on the person screen however the contact still displays on the customer contacts screen when those are selected.  I dont see a column for validity period either or hidden or blocked on the contact screen. we want our reps to know that the inactive contacts are inactive on the contact screen.