This may not be the same reason as i think but most of the time this happens also a lot when joining another server that has the same base script as this server.
As Chase stated this happened to me before, you have to delete EVERYTHING from your resource file and re-join the server so all the scripts can re-download.
Other then the fix that already has been mentioned you could exit MTA, delete everything inside the C:\Program Files (x86)\MTA San Andreas 1.3\mods\deathmatch\resources\ folder and then start up MTA again instead of deleting the resources while running mta
If that doesn't work, i never tried this actually maybe it helps:
Delete everything in the C:\Program Files (x86)\MTA San Andreas 1.3\mods\deathmatch\priv\ folder.
Other things that may could help is, reinstalling MTA or connect to the server with "Quick Connect" in the MTA menu.