Getting the same issue. Worked fine yesterday, today I can't join any high player servers. I tried to connect 10 times and restarted my game each time, but it kept failing. Judging by other people's comments, this issue pops up randomly and then disappears again. Well, I didn't want to wait for it to fix itself.
By the way, I tried the radio thing, just to amuse whoever suggested it, but obviously it didn't work.
The game has problems connecting, so it seems to be connection related. I went to my documents and looked inside the file "rgl_config.txt". There is a line "max_number_of_connections = 16".
I changed it to 8 and I could then join all servers.
I changed it back to 16 and I couldn't join anymore.
I changed it to 128 and most servers didn't show up in the server browser anymore.
The game seems to have problems with high amount of connections. So I lowered it to 12 and now I seem to be able to join most servers just fine.
So, a possible workaround for this issue is to open the file "rgl_config.txt" in your documents. And change the line "max_number_of_connections" to 8.
Note that Windows 7 has two of such files that both need to be modified:
On Windows 7 there are two rgl_config.txt files that both need to be modified. You can find them in the following locations.
I hope it works for you guys too!