Show me your server's start.bat
Doesn't matter.
OP, some addons fail to download because of a timeout and/or filesize limit. Unfortunately, there is no easy way around this.
To resolve this issue, download the addon on your client and locate its corresponding .gma file. Rename this file to ds_<addon id>.gma, the addon ID being the last few numbers in the current file's name. Upload this file to the /addons/ directory on your server, and voila.