I just tested this on a 6.1.12292 instance with the free license type. I joined a Windows guest to a support session and selected "Install Access" from the host page. The access client installed on the guest machine without issue.

How many access clients are calling back to your instance? The free license type allows up to three access clients to call back at the same time.

Also, what is the guest's OS for the support session you are attempting to convert to an access session?

@EnlightenIT So as of 6.2 we've rolled back a few features for the free licenses. When it came down to it, we wanted to give people the ability to use ScreenConnect for personal use but we were seeing a significant amount of business/corporate use; so we had to scale back the feature set a bit. We made an announcement for it here.

With that said, we are not against adding features back to the license if there are enough requests for it. IMO, copy-paste is one of those critical features that we should have, but file transfer is one that we decided we had to restrict. Due to the current architecture, it wasn't feasible to disable file transfer but leave copy-paste available, since they work in basically the same way. With that said, it is not out of the question for us to split them up a bit, or at least add it back. Still, though, I strongly recommend registering a feature request to enable copy-and-paste for free licenses and you can do so here.