When you receive an error 2273 after executing a 'Send Message' command, try this:
1. Click on the Start button.
2. Select the Run menuitem in the Start menu.
3. Now type in the Run dialog: services.msc /s and click 'ok'. (The 'Services' dialog will appear.)
4. Search for the item 'Messenger' and select it.
5. Click on the 'Properties' button on the toolbar.
6. Set the 'Startup type' to 'automatic' and click the 'Start' button.
7. Click the 'Apply' button.

Now retry sending the message.
Microsoft disabled this feature from Windows XP onwards, so it has to be enabled manualy.

Also try to do a 'Net Send' to the XP machine from the command line, if this fails then it will certainly fail via AutoExit also.

For Windows Vista, this feature doesn't work (yet).