curses mystical error output

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I have a fairly simple curses app which is giving me this error:

    addstr() returned ERR

I'm trapping it and continuing.  I can see that *some* of my addstring calls
succeed.  This one happens to be

    screen.addstr(row, 39, "|")

where row is 3.  After the screen was cleared two other calls to addstr
succeeded.  What's wrong with this one?  Can I get a more heplful message
out of curses somehow?  FWIW, I am running on a Mac from a Terminal.app
window which tells me it's an xterm.  I am ssh'd into a Solaris host with a
command like

    DISPLAY=:0 ssh -C -Y -X remote-host

I tried simplifing the ssh command down to

    ssh remote-host

but I still get the error.  I tried setting TERM to "ansi", "vt100" and
"dumb".  Ansi and vt100 failed with the same error.  Curses refused to run
on a "dumb" terminal.  I tried commenting out the particular line (it's just
drawing a boundary between the left and right halves of the window, so I can
live without it).  A later addstr call fails.

Any suggestions?  Do I need to followup addstr with some sort of periodic
flush() call?

Thx,

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