How to fix ROBLOX "Error Code 17"?

According to Roblox's support page:

Signs of Connection Problems

Roblox has trouble with or fails to load online games, sometimes showing the player an error message (which can include "Could Not Connect" or "ID=17 Failure" messages). Loading screen on the website takes a long time or never finishes to load. Player can visit games in the Build or Edit modes, but not in Play mode. Games randomly or consistently tell you that they have shut down.

The site then has you try some basic troubleshooting to resolve that error:

Reset Your Internet Options (Windows Only) Many times, a simple reset of your Internet Options is all you need. Please keep in mind that these steps will need to use Internet Explorer, but will fix many problems even for players that use other browsers such as Chrome or Firefox. Please try the following:

1. Open Internet Explorer (this browser specifically)
2. Open the gear icon > Internet options
3. Open the Advanced tab
4. Click the Reset button
5. Close Internet Explorer
6. Try playing again

Check Your Browser’s Security Settings You will need to ensure that the security settings on your browser allow for Roblox. If these settings are set too high, it can cause a variety of problems ranging from what is listed at the top of this article to website issues such as buttons/links not responding.

Check Wireless Connection You can rule out the wireless connection by switching to a wired connection if possible. If it’s not the connection, or if you can't try a wired connection, then check your firewall's settings, which we will discuss below.

Remove/Disable Any Ad-Blocker Browser Add-Ons Browser Add-Ons/Extensions can cause a number of issues, and in particular, Ad-blockers can stop a game from fully loading.

Make Sure the Appropriate Ports are Open The ports that Roblox uses is dependent on the Operating System used. The port range is currently UDP 49152 - 65535, so keeping all these ports open should allow Roblox to connect to your router properly.

Configure Your Firewall and/or Router A lot of antivirus or internet security software tries to control which programs can access the internet. Often, these programs err on the side of caution and by default no program is allowed access.

Reinstall Roblox

Otherwise, Contact Roblox's support.