I opened a project, created a year ago, and got the attached error message regarding using a newer MassFX file which is not backwards compatible. Nothing in Max 2013 has been changed, but I upgraded both ThinkingParticles and RealFlow to the latest versions. ThinkingParticles is used in the project.
It's just a warning message which you can usually ignore - did you upgrade your 3ds Max version ?
If you are not using MassFX in the scene at all, you can simply ignore the message and resave the scene ( which should get rid of the message ). If this is a scene which makes use of MassFX, check that your simulation still behaves as you want it to do and resave...
Thanks. I resaved and no longer get the error message, but the animation takes way too long. This was not the case before. Any suggestions?