Server crashes after a while for no known reason

[TacticHell]

Hi there folks.
For some reason my GMOD(TTT) server crashes a while for no known reason.
I can't even log in to the server's ssh when it happens and only a power cycle helps.

Server OS: Ubuntu 14.04 x32
Processor: Intel® Xeon® CPU E5-2630L v2 @ 2.40GHz
Ram: 512MB, 20GB SSD ROM
Game(s): GMOD TTT
Start Up Command: /home/*SECRET*/server_1/srcds_run -game garrysmod +maxplayers 24 +gamemode terrortown +map ttt_minecraft_b5 +host_workshop_collection 323143086 -authkey *SECRET* -secure

Admin Mods: ULX
IP: 188.226.176.175

Thanks in advance