I just wanna share a trick to send file from Nokia N900 to other devices. As we know, we have a bug that Nokia never fix it about Bluetooth device. If we realized, we find it difficult to send a file from N900 to PC, BlackBerry (especially OS 5.0 and lower), etc via Bluetooth, we always got "Connection failed to ..." message.
Finally, I found a trick to make it possible. Here is my way:

1. Pair N900 with the destination Bluetooth device (needed by some device).
2. Remove /var/lib/bluetooth/5C:57:C8* using XTerminal or FileBox.
3. Prepare destination device to receive (needed by some device).
4. Send a file!

WARNING! I don't know is this dangerous or not. So, do it at your own risk! Make a backup of the folder if you are worried.
FYI, after we send a file, the folder we've deleted will appear again.