Thank you for your post.
Since this used to work, but no longer works, we can probably agree that something has changed.
My first inclination would be to stop the server and open the file locally with a client. With the local file, see if you can perform a find. If this works, then something has happened with the Server. You may want to stop all databases, quit FileMaker Server and relaunch. If this doesn't work, then perhaps the index is damaged. Go into "Manage -> Database" and turn off the indexing for the field in question, and then perform a find. This will rebuild the index, and you should be able to find the record.
If you still can't find the record, try launching this file on another machine. If it works on the other machine, then your copy of FileMaker Pro may have become damaged, so uninstalling and reinstalling could be a possible solution.
Let me know what you have tried along with the results.
I re-startedthe server and everything is fine. I did not try that earlier because the problem started right arfter installing iLife '09 and I thought the problems was on the client side. Many thanks.