It seems to me, SimMechanics is from MathWorks and the Pro/TOOLKIT application that works as the interface is also maintained by them.
The message (being a Pro/TOOLKIT message) indicates that there is a registry file installed in the Creo toolpath, but the simMechanics application it points to, is not there.
In this registry file (the mentioned file with extension *.dat) there should be references to an executable or a dll (exec_file) and - optional - a text directory (text_dir).
It seems those referenced files are not where they are expected to be.
Either they have not been installed or they are somewhere else.
If you can't solve it by checking and correcting the paths and/or re-installing simMechanics, you probably should check with a MathWorks forum or with their Support.