Usually, when you are working with Maya's dynamics engine, expressions, or pretty much anything that might be "dynamicly" animated, that warning, (or others) tend to appear.

Usually, there is nothing "wrong" it's simply Maya's way of warning you that things may not evaluate, or solve, exactly the same way every run.

Even though it may appear EXACTLY the same every run, it may be even as small as a nano degree off of what it calculated the previous run.

Each warning is different, but if you feel that you want to know more, just do a search for that warning, and it should present you with an explanation for it.