Checking for Equality Occasional Failure

Hello,

I'm doing an Assert.AreEqual on a mocked interface instance. In 2 of 3 test methods, checking for equality on the mock fails. I was curious why that would be... any guidelines for checking equality in this case?

Thanks.

MS Test Result:

Failed Assert.AreEqual failed. Expected:<Mock0000IUnitOfWork>. Actual:<Mock0000IUnitOfWork>.