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Troubleshooting

Q: Metalog runs, but when I give the "Think!" command, it doesn't do anything.
A: Metalog might have trouble to idenfity where SWI-Prolog is installed in your system. This should happen automatically both on Windows and Linux systems, but if it is not working, then the solution is to include in the system variable PATH the directory where the SWI-Prolog executable files are stored. On Windows, another possible cause of trouble can occur if you have installed SWI-Prolog and changed the default file extension (".pl"): in this case, the best thing is to uninstall, and then install again, SWI-Prolog with its default settings.
Q: Metalog runs, but when I give the "Think!" command, the SWI-Prolog window stays open, maybe with some warnings, and nothing more happens.
A: Auch!
This is due to the computational power of Metalog: in some cases, the computation needed to obtain the answer is infinite (!), and as a result, SWI-Prolog never terminates.
The immediate solution is to manually quit both SWI-Prolog and Metalog. SWI-Prolog can be quit by pressing CTRL-C, and then pressing "a' (for abort). After this is done, Metalog might return back to normal: if not, then you need to quit it as well. Depending on what Metalog executable you are using, you would need to either press CTRL-C, or to forcefully quit the program.
The long-term solution (fix) varies. In many cases, not all the answers are needed, but just one: therefore, you can change the Metalog configuration, setting it so to return just one answer to the query. Then, try again making Metalog think. If this does not help, then sometimes it is sufficient to change the Metalog discourse (for instance, by switching the order of some assertions, or by slightly changing the logic), but this requires a certain skill. In other cases, this is intrinsic to the complexity of the problem, so even if you are skilled there is not much that you can do. Note that this also depends on the particular engine that Metalog is using: different engines, for instance, could successfully terminate whenever SWI-Prolog doesn't. In the future, Metalog might interface to different inference system, therefore providing better solutions to this computational problem.
Finally, unlikely in this case but not impossible, note that this could also be a Metalog bug: in doubt, please submit a bug report to metalog@w3.org.
Q: I am puzzled: when installing SWI-Prolog, several options appear; what kind of install should I use?
A: You can use any kind of install you want, so even the very compact minimal installation. On Windows systems, the only constraint to remember is not to change the file extension of SWI-Prolog files, which should stay the default ".pl" . Even if you have installed SWI-Prolog in the wrong way, you can always uninstall it, and then install it again (for example, to save a lot of space by reinstalling it with the minimal install); in this process, you do not need to uninstall Metalog.
Q: On Windows, nothing appears when I try to launch Metalog.
A: This should only occur when running Metalog from the source distribution. Likely, it means that the wxPython package has not been installed properly. Notes that wxPython comes in different versions, according to the Python version that you have installed: so, be also sure that you have installed the correct wxPython version. As said, note that this problem should anyway not occur if you have used the automatic installer.
Q: The keyboard shortcuts sometimes don't seem to work.
A: This is not a Metalog bug, but a focus mismatch in the windows handling system. Just click everywhere inside the main Metalog window, and the shortcuts will then work.
Q: When checking correctness, Metalog tells me the file is not a Metalog one.
A: did you remind to save the file using an ".ml" extension? If this doesn't solve the problem, then quit Metalog, then launch it and reopen the file, this should fix it.
Q: Metalog doesn't seem to work well any more, for instance checking correctness doesn't do anything.
A: There might be an error in the syntax, or a bug, from which Metalog couldn't easily recover: if you are running Metalog in a mode where the console is visible, you should be able to see the error there. Check carefully that the Metalog program is correct. In any case, Metalog might have become unstable, so it is wise to quit it and then launch it again.
Q: When I try to do something on a Metalog discourse that I just saved, Metalog tells me it is not a Metalog file and can't work on it.
A: This can sometimes occur if you created the file directly with the Metalog editor using the "New" option under the "File" menu. First, check that you saved the Metalog discourse with the file extension ".ml". If this still doesn't solve the problem (or, it was not the case), then the quickest thing is to open another discourse, and then reopening the original discourse should work. Alternatively (but longer) you can quit Metalog and then launch it again: opening the discourse should then work.