Why does my sever frezees whe using OWA????

[rocketlauncher]

Hello Everyone!

I have an issue here, hope someone can help me with this one.

The thing is that when a user tries to access his mailbox remotely (from another city through dialup connection) , my exchange server freezes up. I look for some clue in the event viewer an all I can see is the following:
"Previous shutdown was unexpected"

This happens time an time again.

Does any one have clue, why does this happen??? or what causes it?? If so what can i do, to prevent it from happening??

Thanks in advance for your help.

Best regards,
Rocket.