It's a common problem I guess. Disable the limit for the nade modes. By default, each nade mode is limited to 5. I remembered I had the same problem with you. I don't know if it actually works. It's quite a long time ago so I don't know if that fixes the problem.
EDIT: Some server owners don't even know about the commands in the nade modes. You can access the menu by going to console and type "amx_nmm". Make sure you have required admin to use the menu.
Just browse through the menu and you will eventually see a limit setting.
Last edited by Excalibur.007; 12-29-2011 at 08:32.