You did not put part
/config=Release
inside your quoted team text.
Your team should look like
"c:\Program Files\NUnit 2.4.8\bin\nunit-console.exe /config=Release C:\projects\IntegrationTests\IntegrationTests.nunit" 2>&1
... I did not check the nunit-console.exe command line options, but suppose you already tested if the nunit command works.
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