You do mean the "Check with BibTeX" button right? Could you reproduce it again by removing texlive-bibtexextra and doing the action that triggered the error? I ask because I am unable to reproduce this myself, but files from the package do match keywords in the source:

for i in `pacman -Ql texlive-bibtexextra | awk '{print $2}'`; do [[ -f $i ]] && grep -Rw "`basename $i`"; done

I have used the check feature numerous times but I have always had the whole texlive gamut on my system, so good catch nonetheless. Most probably this is because the bib entry or entries you are checking require the apacite or harvard styles.

yes, its that button i mean.
i cannot reproduce it failing anymore, with or without texlive-bibtexextra.
(but yesterday it failed albeit bibtexextra was installed).
mysterious, i'll keep trying.

the error happend again, and since the text in the dialog is not copyable (and ocr failed) i just provide screenshots of the error message.
texlive-bibtex is not installed atm, but it seems not related, since it also happend once with texlive-bibtex installed.
i hope this helps.

Is it possible for you to share privately (e-mail) or publicly (attach) this particular bib file? This could be bib-specific (your particular bib file), or it could be upstream in either bibtex (less likely) or kbibtex (more likely).

Remy, adding you in case the answer is obvious to you from the bibtex output.

this is the file in question.
it was started with kbibtex and never edited outside of it.

Could you use this file and see if you can reproduce the error(s)? Otherwise, I'm drawing a blank, since (i) you say this happens regardless of the presence of bibtexextra, and since (ii) I have also tried to reproduce this by uninstalling everything else, to no avail.

The original bib file you attached seems to work here. Checking the entries one by one (right-click > Edit Element > Check with BibTeX) reveals the warnings of the entries (missing chapter, journal etc.), but there is no bibtex process error.

Let me walk through the steps again to confirm that I am doing what you are doing. Open the bib file with kbibtex > right-click on an entry, e.g. iancu2012 > click Edit Element > click Check with BibTeX > receive a kdialog saying errors were found, in particular "field journal is empty".

after restarting the program this file works, as well as my original file.
how can this be related ts restarting the program?
sadly i forgot to test your file without restarting. i will do as soon as the problem reoccurs.

The tex stuff is a result of decades of work, so I'm giving them the benefit of the doubt. Any problem is certainly to be a problem with the input, which is prone to human error.

Since you say the bib file was created from within the program and never edited, I'd have to say it's the program acting up here (probably some race condition not accounted for, or a parsing gone wrong).

The main error is in the input to bibtex. Also, since here it appears to work with only base texlive, it is very likely not a packaging issue.

If I were you, I'd take a look at the temp files (you can look at the log carefully once the error occurs again to see which file was processed last by a command).

Note: The test file I provided contains bogus values to populate fields, so don't use it for anything other than testing. You should also report this upstream in the meantime.