This message comes directly from the database (H2) used inside Ubooquity. 

I didn't know such a tool existed, but I found the part of H2 documentation that explains how to use it:

https://www.h2database.com/html/advanced.html#using_recover_tool

I did not try it though.

Thanks a lot for the thorough analysis !

I'd prefer to find a way to save bookmark when the page is closed rather than using a timer. So I'll probably try to use pagehide and visibilitychange events in addition or instead of beforeunload.

I don't have any iOS device though, I'll need some help testing the workaround when it's developped. :)

Oh, that rating.

Nothing planned for that yet, but that's a good idea I'll write it down.

Indeed I misread. I'll look into it.

Then i upgrade java for the last version and now i have:
G:\Ubooquity 3>java -version
java version "1.8.0_411"

You have the latest version of Java 8.

You need at least Java 17 to run Ubooquity 3.

For Windows you can use this one (but other exists, any Java 17+ should be fine): 

https://adoptium.net/en-GB/temurin/releases/?os=windows&arch=x64

I have added a "user rating" column in the database in version 3 (just in case) so that one day user can rate their books, but I don't know if and when I'll implement this feature.

That's by design: shared folder must be distinct, one cannot contain another.

Thanks to the file you sent me I was able to reproduce the issue and fix it. 

The fix will be in the next minor verion (3.0.3). :)

Thanks for the bug report.

I just did a few changes to the PDF rendering part to fix another bug. So you can either wait for Ubooquity 3.0.3 that will include these changes to check if your issue is fixed, or (even better) send me some examples of PDF file that triggers this error so that I can investigate them directly. My email: tom at vaemendis dot net.