Merci for your time Chet. As for your question suggestion :"to add "CET" for the timezone in your data", I'm not sure I understand exactly what you want me to do. I must say I've tried everything possible: even rewritten manually the dates in any possible format, American or French. The problème is Java overwrites the system date (CEST), whatever the files date format or the Study folder date format be. I just even tried to add a vba Module to a rejected excel file to force the CET time instead of the system CEST. Please see the Notepad file attached. No change in the outcome. Still CEST timezone is read. Same error msg with our own research data or Labkey demo data.
I should add that in my Study configurations I always change the CEST default time to CET, still the error CEST msg appears when submit to the import to the database !

The odd thing is that this Java behaviour with european time zone is not the same from file to file! Demographics.xls file with an identical Date field format is imported to Labkey server while the same structured file LabResults.xls produces the CEST error msg! Maybe in the first, the system is not parsing on date while in the second it does.
I'm thinking of abandoning Study feature and try other type of project types like Lists, but it's a pitty as we lose all the UI and prebuilt features for Study type (clinical research, cohorts, ...).
Would you please let me know if there's another French or Center Europe Labkey customer? I can maybe try to see how they deal with this specific problem.
Hopefuly this bug will be fixed in the coming version.
Panthéa