If you are having problems with multiplayer check the GTA2 multiplayer FAQ page.
For save game crashing look at this trailer kill frenzy fix
Q: How do I stop the text at the bottom of the screen from being cut off?
A: You can either run the game fullscreen or go to your Windows display settings and make sure the font scaling is set at 100%.
Q: How do I save the game?
A: Get $50,000 and then go to the church. It is usually in the middle of the map. It has a Jesus Saves sign. TV vans point the way. You start there at the start of the level or when you load a game.
Q: I cannot run in Windowed Mode, why not?
A: Install Vike’s GTA2 patch or set your desktop colour depth to 16bit.
Q: How do I fix a 16x16x16 Video Mode error?
A: Try running GTA2 Manager in Windows 98 compatibility mode (right click gta2manager.exe and go to compatibiliy tab). You could also try fullscreen instead of window mode. Sometimes a reboot will fix it.
Q: Why is the frame rate so low? How can I speed up GTA2 singleplayer?
A: Import this registry key. That registry key creates HKEY_LOCAL_MACHINE\SOFTWARE\DMA Design Ltd\GTA2\Screen and the key min_frame_rate with value to 1. It also creates a key for GTA2 v11.3 and newer: HKEY_CURRENT_USER\SOFTWARE\DMA Design Ltd\GTA2\Screen and the key min_frame_rate with value to 1.
If that doesn’t work, you should try running dxdiag.exe and changing Windows Video Hardware Acceleration from full to basic. Sound Acceleration may also need to be lowered.
Q: Why is GTA2 running super fast speed?
A: This can happen if the frame rate limiter is disabled. Run GTA2 manager, go to the video tab and in the Frame Rate Control, tick Frame Rate Limiter.
Q: How do I change the radio station in the PC version of GTA2?
A: Push F1 to cycle the radio stations one way and F2 to cycle the other.
Q: I can’t hear the Radio stations, or the Radio station is too LOUD, what controls Volume?
A: Push F3 to decrease volume, push F4 to increase volume. *In multiplayer games, any player changing this setting to their client also changes the other players Radio Station attributes.
Q: Why do I get “Security failure” when running GTA2 in singleplayer?
A: This is a problem with the game detecting the CD. I recommend switching to a free version that doesn’t require a CD
Q:Why do I get this error? Cannot open file : test/replay.rep
A:Run GTA2 Manager, click on the debug tab and untick “Play Replay”. You also need to make sure your GTA2 folder is writable. It is best not to install in Program Files since Windows often protects that folder.