Why would putting in the default gateway cause exchange 2007 to crash?

A little background:
Running Exchange 2007 SP1 on a Dell 2970 Poweredge with Windows server 2008 R1
The exchange server is a single box, CAS and Hub transport all in one.  No edge server on network.

We had some hardware issues with another Dell 2970 that was causing the system to crash.  Eventually we traced it to bad Ram but several crashes caused some exchange database problems.  We fixed everything and got the system up and running on a new identical Dell 2970.  Everything was running great until we went to enable OWA again.  The only problem is now, the system will automatically restart every 30 mins or so because the Dell system manager detects a hung operating system.  Seems different than before and only happens when a default gateway is filled out for the NIC.

My question is really - what might be causing this?  Without the gateway information, exchange works fine except for OWA.  Internally and external mail flows fine when you're on the same network as the server.  Only when you get outside the building do you need to connect to owa so the default gateway is needed.  What could cause a server to crash only when default gateway information is supplied?

Thanks for the help,
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I don't think entering the default gateway on the NIC is causing your problem my guess would be that you have some problem within OWA that is causing this issue.  Do the application logs on the Exchange server show any errors other than the Dell system manager?
Suliman Abu KharroubIT Consultant Commented:
also it could be a fault hardware (embedded NIC), did you tried to use the second NIC the server. also a NIC driver ? is i last updated ?
ccmadminsAuthor Commented:
Update - Never able to find the cause of the problem  Ended up removing the CAS role from the server and installing onto a different server.

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ccmadminsAuthor Commented:
Could not find the cause of the problem, just had to remove and reinstall exchange roles
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Windows Server 2008

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