I had to Force Quit openoffice.org for some reason. After I did this, the hostname of my laptop changed 
due to picking up a new hostname via DHCP when I connected it to a network. When I then tried to 
reopen openoffice by double-clicking on a presentation file on the desktop, two problems occurred:

1. A dialog appeared saying:
"Either another instance of OpenOffice.org is accessing your personal settings or your personal settings 
are locked.
 Simultaneous access can lead to inconsistencies in you personal setings."

etc. etc. I believe this is due to the hostname change.

Maybe this dialog is harmless in this situation - I don't know. I just chose to continue, as I was in a rush 
to give the presentation.

2. OpenOffice did not open the document. It just sat there - no error message, nothing. I had to use 
Open twice(!) from the File menu before it actually managed to open the document succesfully, and 
even then it only opened it read-only, and complained that the document is open on another computer 
(it thinks the old hostname represents a different computer, I presume).

My experiments have revealed that restoring the old hostname and restarting openoffice works around 
this problem - as usual, you get prompted to start recovering the document (which had been open 
when I used Force Quit, by the way), and it opens the document without problems.