Timeouts during unit tests

When I select a class to run everthing works fine. However when I select multiple classes to unit test, I am getting timeout issues. I can run the individual test for each class fine. Anyone know why it's timing out when I select a larger number of tests to run? ( By large I mean around 200 )

It doesn't appear to be any one test. The same test will pass on one test run and timeout on another. Once I hit a test that'll timeout, all subsequent tests will also timeout.

[487 byte] By [JohnD90] at [2007-12-24]