These types of errors are typically caused by formatting problems in the mechanism. To debug these, start by manually inspecting the Chemistry data. Usually Chemistry data is ok unless there are some references with strange characters or missing END statements (It is recommended to delete the references at the initial stage to save time). The thermodynamic data file is almost always the problem when it comes to formatting. typical Issues are: a) Extra thermo data. This is always a 5th entry on line 4, which Chemkin ignores, but a warning will be issued for each specie b) Coefficients formatted improperly. The required fornat is 5(E15.8) for lines 2 and 3 of each specie and 4(E15.8) for line. Deviations from this are not tolerated. Formatting any other way else will cause a seg fault. c) Missing ending line number d) Hidden characters such as tabs (these are the hardest to find, so it is important to use a suitable text editor).