AFAIK, there’s no way to find that out. Try looking for the lock file and delete it.
Thanks for your answer, Bob.
Sad. I already tried to find that file, but it's tedious: the ICML file was used in at least 12 manuals and each manual has two or three published revisions plus the layout stages, which sum up to something like 150 INDD files in total.
I really would be great to have a log file or data base or call-it-what-you-like, in which ALL occurences of one ICML file are stored. Or, even better: It should be stored WITHIN the ICML itself!
BobLevine is right, the file is on the same location as the ICML file.
The file is hidden so you might not be able to see this. Turn on `Show hidden files` in your OS and you would be able to see a fill called something along the lines of `~docname~kwi4s-.idlk` Just delete that one. You can find the location of your ICML in your links panel.