Hi natapol,
that SCORM message doesn't directly depend on your web server configuration but on the network quality in between the user and the (web) server.
If it always appears regardless the user then you've roughly two options:
- serious bandwidth/load issues in your web server
- you're denying serving plain TXT files - which what is used by SCORM (Moodle) to check the network connection availability (/lib/yui/build/moodle-core-checknet/assets/checknet.txt); which turns out to be your case since you deny access to any TXT file but from an enlarged Class C (allow 192.168.0.0/16; while usually a Class C would be /24)
The only other notable thing in your nginx configuration is that you're still using url rewriting instead of a native PATH_INFO support but this is something unrelated.
HTH,
Matteo