I ran into this problem too.
Ok... since Google ranked this discussion pretty high on the results for this error: "Cannot open pseudo-tty" when I tried that to resolve my problem, I'll post what I did to fix my tty problem here.
I had installed Unixtree as root, and I got a wierd error with a frozen pcxterm window when I ran it as non root user john. I had setup an icon to run it with on the desktop. So I ran it from a Konsole terminal and it gave me the same could not open pseudo-tty message you have discussed here. It turns out to be a simple fix for me.
If you check which groups you are a member of using `id' you will probably not see tty in the list.
When logged in as root:
I added john to the tty group, or tty to john's group membership list...
first by checking what john was a member of... using the `id' command.
Here is what mine showed:
uid=1002(john) gid=100(users) groups=100(users),4(adm),11(floppy),17(audio),18(v ideo),19(cdrom)
Then using the usermod command with a complete list (with no spaces, and comma separated ) so it would not subtract one that was missing(just in case) like this:
usermod -G users,adm,cdrom,floppy,audio,video,tty john
This fixed Unixtree's pcxterm after I logged out completely, and logged in again. I probably should have a better list of groups for john to be a member of... wheel maybe should be there too. I have alot more to learn but this gave my program the ability to run.
Hope this helps.