[Konstantinos]

The first thing comes to my mind is random function with a negative or zero value as parameter. Instead of guessing and searching what custom function that was called in OnPlayerSpawn has 2 parameters (playerid, something_else), you can compile with debug info* and get the exact line.

*Create pawn.cfg file (if you cannot get the extension, copy-paste server.cfg and rename it) into pawno folder and write -d3 in it. Re-compile your script (mss.pwn) and reproduce it to get the new results.