...and it indirectly demonstrates that all stored effects are read once, at launch.
If you don't know which effect is incorrectly written, you can try checking modification dates and isolating suspects. If that doesn't work, you can arbitrarily divide your effects into a folder the sim does not recognize, using a scheme, alphabet, for example, until you find the culprit.
Once located, the error will be in the minimum/maximum value for a condition. For example, you may have an emitter delay of .6 and .05. This will throw an error, because .6, as a minimum value, is greater than .05, the maximum value, which is a mathematical impossibility. If you use the in game FX editor, it does not allow you to save un executable values, however, if you manually write effects into the effect folder, the warning message is your only protection.
The sim will still run and it will still load the effect, however, it ignores the erroneous condition and informs you of this state with the error message.