Comment 1 for bug 1278599

That file may contain personal information, so I can't ask you to put it on the Internet. I'll work on a script to diagnose loading failures instead.

You can try this as a workaround, while still keeping the broken file around:
$ killall onboard
$ mv ~/.local/share/onboard/models/user.lm{,.broken-2010-02-10}
$ cp ~/.local/share/onboard/models/user.lm{.bak,}
$ onboard

This reverts the word suggestions to the last known-good state and the error should no longer appear.