I was working on my thesis and everything is fine and works as ist should.
Then I realized that this is written in the log file:

The document still works fine but I do not understand what it wants to tell me or what the actual problem is since I do not remember changing anything. Do I have to worry about that. What did I wrong?
I am using this biblatex package:
\usepackage[backend=bibtex,style=authoryear,natbib=true, maxbibnames=99, maxcitenames=1]{biblatex}
\addbibresource{bibliogrpahy.bib}
Can anyone help me understanding the problem?

biblatexwarning about the BIbTeX backend will always (well at least for a few years) have been there. And it means pretty much what it says: You are using BibTeX and not Biber, but with BibTeX not all features ofbiblatexare available. It is recommended you switch tobackend=biber,and run Biber instead of BibTeX (https://tex.stackexchange.com/q/154751/35864). – moewe Aug 06 '21 at 05:31fig:Label1for different figures. Of course that does not go down well with LaTeX since it cannot know which of the several figures you mean when you now say\ref{fig:Label1}. Use each label only once and consider using more semantic names likefig:catandfig:mouseinstead of numeric labels likeLabel1. – moewe Aug 06 '21 at 05:32backend=biberI just wonder why it comes now and never before. Also the second problem never apperead before and I did not add a new label. I went all all them trough so far I did not find any identical labels. But thanks I will try. – Roland Aug 06 '21 at 05:40biblatexwarning has been implemented inbiblatexfor a long time. If you did not update recently and did not change yourbiblatexsettings recently, the warning will have always been there. But it is possible that your editor hid the message from you until now. See https://tex.stackexchange.com/q/25701/35864 for some background on the terminology (and also https://tex.stackexchange.com/q/63852/35864). – moewe Aug 06 '21 at 05:42.aux,.bbl,.bcf,.toc,.lof,.lotfiles and recompiling from scratch (do not delete any files ending in.tex,.bibor graphic files). – moewe Aug 06 '21 at 05:43I found no \citation \bibdata \bibstyle commands– Roland Aug 06 '21 at 06:03backend=bibtex,tobackend=biber,? In that case you need to run Biber and not BibTeX (see my comments and links above). If you stuck withbackend=bibtex,keep in mind that you first need to run LaTeX (and the run should finish without errors) before you can run BibTeX. The LaTeX run needs to write the necessary auxiliary files for BibTeX. – moewe Aug 06 '21 at 06:05