Avoid Session Timed Out Issue in NetSuite

There are two other ways that session cookies can be blocked either or both might apply to you:

Web Browsers
Web browsers can also block session cookies but this is easily fixed.

Note: It is important to close all browser windows after making the change suggested below then open a new window for the new setting to be active.

Internet Explorer:
(Some users resolved the problem by using the setting below)
1. Click the Sprocket in the upper right, and select Internet Options.
2. Click the Privacy tab, and select Advanced.
3. Click Override automatic cookie handling.
4. Click Accept First Party Cookies
5. Click Accept Third Party Cookies
6. Check Always allow session cookies to always allow session cookies (cookies that will be deleted from your computer when you close Internet Explorer) to be saved on your computer
7. Click OK
8. Click OK

Mozilla Firefox:
1. Click the three Bars in the upper Right. 
2. Click Options
3. Select the Privacy & Security Tab
4. Set Firefox will: to Use custom settings for history
5. Check mark Accept cookies from sites to enable Cookies
6. Accept third-party cookies: Always
7. Keep until: they expire
8. Close the Open Menu Tab.

Google Chrome:
1. Click three dots in upper right corner.
2. Click Advanced
3. Under Privacy and Security > Click Content Settings
4. Click Cookies
5. Select Allow sites to save and read cookie data.
6. Disable Block third-party Cookies.
7. Ensure netsuite.com is not listed in the Blocked cookies list.

Firewalls
Firewalls (personal or corporate) can remove a session cookie very soon after it is created. This means that the web site can make the session cookie but it is destroyed by the firewall.

Firewalls that affect session cookies will not only stop user from using NetSuite but also many other web sites where you login to gain some level of access.