Hi 
Sounds painful! Please could we have a few more details?
1. When does the error message appear? Does it appear when the machine boots-up (switches on) or when you try to open a file/document using LibreOffice?
2. Can you still use other programs on that machine, such as opening the web-browser or playing a simple game or viewing photos?
3. What did you re-install? Was it LibreOffice? Did you get the download here
http://www.libreoffice.org/download/
(There are other legitimate places to get it from but so far i have only used 2)
If you did get it from there did you change the first drop-down to Mac OS X ppc or intel?
4. When you deleted the preferences did you do that from a file-browser to navigate to the
/Users/<user name>/Library/Application Support/LibreOffice/
folder to delete the "3" folder (or the whole "libreoffice" folder either should do the trick.
5. Have you tried opening a different document, other than the one that went wrong?
6. Have you tried opening one of the other LibreOffice apps from the Mac menus rather than opening by clicking on a document?
Regards from
Tom 