There are some known bugs that players under the same CD Key won't be able to join the same server at the same time (Original from Gamespy).
The masterserver allows all CD Keys you type, so make sure to have a different one from your friends.
Here are some CD Key examples:

3E67-7DA-FB5-0E06-EU20
20F1-609-C13-94E3-EU20
397B-7A4-F49-D38B-EU20
1F8F-58E-B1D-63E2-EU20
C83F-BB0-E05-57FF-EU20
139d-236-083-e4ce-eu40
4711-4ef-0c4-1b2d-eu20
ca37-8f8-e7b-dfa3-eu20
0334-47B-8F6-F437-EU20
4A5D-06F-0DF-5747-EU20
6387-2AA-555-3594-EU20
56BD-19F-33F-A9D8-EU20
3273-700-E01-98D4-EU20
362A-74C-E98-E035-EU20
2FA1-6E1-DC3-A617-EU20


**To change your CD Key go to Install/CDKey.exe and put one of the previous ones or a similar one**


If you need more help, send me an email or reach me in Discord!

Anyder#9802
communityambassador@swbfgamers.com

 - Anyder - dir, Operations Excellence & Communication - SWBF & Player Engagement