There is no ReplayMod 2.0.0 (I assume you use the beta builds).
We can't provide support for replay files not generated by our software, all kinds of things might be broken, unless the author of said 3rd party recorder can either convince us that his software is correct or can point us directly at what needs fixing.
As for the error you got, there almost certainly has to be a stacktrace. Please also check all the other log files (Forge logs into three or four files iirc).