Click the re-login button (») before you try to join:
If this does not help: quit CS2D Change your account password at this website Re-start CS2D and change your account password there as well Wait for login and try to join again
Still not working? Quit CS2D Wait 15 minutes Try again
Have you tried deleting USGN.dat file and replacing with a new one? You can get the new USGN.dat by downloading the CS2D zip archive from the main website and extract the new USGN.dat file. You can get that file from sys folder and replacing it to the same folder (sys) from your CS2D folder. When you're done, give a try to see if is working now, however I am not sure if it'll fix the issue...
@ Tonic: Go to mediafire (or any other site) and upload your cs2d folder but skip the gfx and sfx files (also log off before you give it to me) Ill see if its on the cs2d folder or your computer.